Program.cs

using System;
using System.Security.Cryptography;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

namespace StringTestsCore
{
    [CoreJob, MinColumn, MaxColumn, RPlotExporter]
    public class LowerTrimSwitchVsTrimEquals
    {
        [Params("first","third","default","FIRST", "THIRD", " first ", " third ", " default ", " FIRST ", " THIRD ", "         first          \n", "          third          \n", "          default          \n", "          FIRST          \n", "          THIRD          \n")]
        public string str { get; set; }
        
        [Benchmark(Baseline = true)]
        public int LowerTrimSwitch()
        {
            var str2 = str.Trim().ToLowerInvariant();
            switch (str2)
            {
                case "first":
                    return 1;
                case "second":
                    return 2;
                case "third":
                    return 3;
                default:
                    return 0;
            }
        }

        [Benchmark]
        public int TrimEquals()
        {
            var str2 = str.Trim();
            if (str2.Equals("first",StringComparison.OrdinalIgnoreCase))
                return 1;
            else if (str2.Equals("second", StringComparison.OrdinalIgnoreCase))
                return 2;
            else if (str2.Equals("third", StringComparison.OrdinalIgnoreCase))
                return 3;
            else
                return 0;            
        }

        [Benchmark]
        public int IndexPropertyDirectlyGte()
        {
            if (str.IndexOf("first", StringComparison.OrdinalIgnoreCase) >= 0)
                return 1;
            else if (str.IndexOf("second", StringComparison.OrdinalIgnoreCase) >= 0)
                return 2;
            else if (str.IndexOf("third", StringComparison.OrdinalIgnoreCase) >= 0)
                return 3;
            else
                return 0;
        }

        [Benchmark]
        public int IndexPropertyDirectlyGt()
        {
            if (str.IndexOf("first", StringComparison.OrdinalIgnoreCase) > -1)
                return 1;
            else if (str.IndexOf("second", StringComparison.OrdinalIgnoreCase) > -1)
                return 2;
            else if (str.IndexOf("third", StringComparison.OrdinalIgnoreCase) > -1)
                return 3;
            else
                return 0;
        }

        [Benchmark]
        public int IndexPropertyDirectlyNeq()
        {
            if (str.IndexOf("first", StringComparison.OrdinalIgnoreCase) != -1)
                return 1;
            else if (str.IndexOf("second", StringComparison.OrdinalIgnoreCase) != -1)
                return 2;
            else if (str.IndexOf("third", StringComparison.OrdinalIgnoreCase) != -1)
                return 3;
            else
                return 0;
        }
    }

    public class Program
    {
        public static void Main(string[] args)
        {
            var summary = BenchmarkRunner.Run<LowerTrimSwitchVsTrimEquals>();
        }
    }
}

results.md

BenchmarkDotNet=v0.11.3, OS=Windows 10.0.17134.523 (1803/April2018Update/Redstone4)
AMD Ryzen 7 1700X, 1 CPU, 16 logical and 8 physical cores
.NET Core SDK=2.2.200-preview-009648
  [Host] : .NET Core ? (CoreCLR 4.6.27207.03, CoreFX 4.6.27207.03), 64bit RyuJIT
  Core   : .NET Core 2.1.7 (CoreCLR 4.6.27129.04, CoreFX 4.6.27129.04), 64bit RyuJIT

Job=Core  Runtime=Core  

Method	str	Mean	Error	StdDev	Min	Max	Ratio	RatioSD
LowerTrimSwitch	** (...)
[26]**	77.11 ns	0.2697 ns	0.2391 ns	76.89 ns	77.62 ns	1.00	0.00
TrimEquals	(...)
[26]	68.82 ns	0.3867 ns	0.3617 ns	68.18 ns	69.39 ns	0.89	0.01
IndexPropertyDirectlyGte	(...)
[26]	53.91 ns	0.2505 ns	0.2343 ns	53.41 ns	54.34 ns	0.70	0.00
IndexPropertyDirectlyGt	(...)
[26]	53.86 ns	0.2021 ns	0.1890 ns	53.56 ns	54.15 ns	0.70	0.00
IndexPropertyDirectlyNeq	(...)
[26]	53.85 ns	0.3243 ns	0.3033 ns	53.46 ns	54.42 ns	0.70	0.00
LowerTrimSwitch	(...)
[26]	84.55 ns	0.1756 ns	0.1467 ns	84.23 ns	84.70 ns	1.00	0.00
TrimEquals	(...)
[26]	98.49 ns	0.3723 ns	0.3482 ns	97.95 ns	99.14 ns	1.16	0.00
IndexPropertyDirectlyGte	(...)
[26]	219.65 ns	0.9091 ns	0.8504 ns	218.32 ns	221.35 ns	2.60	0.01
IndexPropertyDirectlyGt	(...)
[26]	219.69 ns	1.0140 ns	0.9485 ns	218.04 ns	221.69 ns	2.60	0.01
IndexPropertyDirectlyNeq	(...)
[26]	219.70 ns	0.7732 ns	0.7233 ns	218.79 ns	221.52 ns	2.60	0.01
LowerTrimSwitch	** (...)
[28]**	68.93 ns	0.5038 ns	0.4713 ns	68.26 ns	69.79 ns	1.00	0.00
TrimEquals	(...)
[28]	66.51 ns	0.3154 ns	0.2950 ns	66.02 ns	67.00 ns	0.97	0.01
IndexPropertyDirectlyGte	(...)
[28]	267.88 ns	1.4330 ns	1.3404 ns	266.14 ns	270.89 ns	3.89	0.03
IndexPropertyDirectlyGt	(...)
[28]	267.92 ns	1.4280 ns	1.1924 ns	265.51 ns	269.39 ns	3.89	0.03
IndexPropertyDirectlyNeq	(...)
[28]	268.46 ns	0.8635 ns	0.7654 ns	266.87 ns	269.84 ns	3.90	0.03
LowerTrimSwitch	** (...)
[26]**	73.75 ns	0.3459 ns	0.3236 ns	73.07 ns	74.21 ns	1.00	0.00
TrimEquals	(...)
[26]	99.26 ns	0.4967 ns	0.4646 ns	98.57 ns	100.15 ns	1.35	0.01
IndexPropertyDirectlyGte	(...)
[26]	219.45 ns	0.6847 ns	0.6405 ns	218.41 ns	220.44 ns	2.98	0.01
IndexPropertyDirectlyGt	(...)
[26]	219.51 ns	0.8189 ns	0.7660 ns	218.46 ns	221.05 ns	2.98	0.02
IndexPropertyDirectlyNeq	(...)
[26]	219.58 ns	1.1543 ns	1.0797 ns	218.32 ns	221.68 ns	2.98	0.02
LowerTrimSwitch	** (...)
[25]**	66.28 ns	0.3865 ns	0.3426 ns	65.78 ns	67.09 ns	1.00	0.00
TrimEquals	(...)
[25]	67.88 ns	0.3148 ns	0.2945 ns	67.44 ns	68.30 ns	1.02	0.01
IndexPropertyDirectlyGte	(...)
[25]	51.99 ns	0.3859 ns	0.3421 ns	51.42 ns	52.65 ns	0.78	0.01
IndexPropertyDirectlyGt	(...)
[25]	51.39 ns	0.2356 ns	0.2088 ns	51.08 ns	51.66 ns	0.78	0.01
IndexPropertyDirectlyNeq	(...)
[25]	51.57 ns	0.2750 ns	0.2572 ns	51.12 ns	52.11 ns	0.78	0.01
LowerTrimSwitch	** FIRST **	54.77 ns	0.2920 ns	0.2589 ns	54.35 ns	55.31 ns	1.00	0.00
TrimEquals	FIRST	44.72 ns	0.3405 ns	0.3185 ns	44.29 ns	45.34 ns	0.82	0.01
IndexPropertyDirectlyGte	FIRST	32.80 ns	0.1701 ns	0.1421 ns	32.55 ns	33.05 ns	0.60	0.00
IndexPropertyDirectlyGt	FIRST	32.70 ns	0.0973 ns	0.0863 ns	32.55 ns	32.82 ns	0.60	0.00
IndexPropertyDirectlyNeq	FIRST	32.74 ns	0.1069 ns	0.0948 ns	32.61 ns	32.97 ns	0.60	0.00
LowerTrimSwitch	** THIRD **	62.01 ns	0.3803 ns	0.3558 ns	61.27 ns	62.64 ns	1.00	0.00
TrimEquals	THIRD	69.11 ns	0.1868 ns	0.1747 ns	68.88 ns	69.43 ns	1.11	0.01
IndexPropertyDirectlyGte	THIRD	88.41 ns	0.2967 ns	0.2630 ns	87.82 ns	88.86 ns	1.43	0.01
IndexPropertyDirectlyGt	THIRD	88.44 ns	0.4706 ns	0.4402 ns	87.76 ns	89.29 ns	1.43	0.01
IndexPropertyDirectlyNeq	THIRD	88.54 ns	0.2695 ns	0.2389 ns	88.09 ns	88.92 ns	1.43	0.01
LowerTrimSwitch	** default **	44.66 ns	0.2181 ns	0.2040 ns	44.38 ns	45.05 ns	1.00	0.00
TrimEquals	default	44.60 ns	0.2169 ns	0.2029 ns	44.21 ns	44.93 ns	1.00	0.01
IndexPropertyDirectlyGte	default	96.83 ns	0.6400 ns	0.5986 ns	95.51 ns	97.97 ns	2.17	0.02
IndexPropertyDirectlyGt	default	96.63 ns	0.4287 ns	0.4010 ns	96.03 ns	97.22 ns	2.16	0.01
IndexPropertyDirectlyNeq	default	96.65 ns	0.6098 ns	0.5705 ns	95.63 ns	97.52 ns	2.16	0.02
LowerTrimSwitch	** first **	43.48 ns	0.2256 ns	0.2110 ns	43.09 ns	43.83 ns	1.00	0.00
TrimEquals	first	43.38 ns	0.3062 ns	0.2865 ns	42.85 ns	43.96 ns	1.00	0.01
IndexPropertyDirectlyGte	first	32.86 ns	0.1898 ns	0.1775 ns	32.61 ns	33.23 ns	0.76	0.01
IndexPropertyDirectlyGt	first	32.65 ns	0.0985 ns	0.0922 ns	32.48 ns	32.81 ns	0.75	0.00
IndexPropertyDirectlyNeq	first	32.72 ns	0.1816 ns	0.1699 ns	32.43 ns	33.07 ns	0.75	0.01
LowerTrimSwitch	** third **	50.20 ns	0.4543 ns	0.4249 ns	49.33 ns	50.64 ns	1.00	0.00
TrimEquals	third	70.02 ns	0.4631 ns	0.4332 ns	69.45 ns	71.08 ns	1.39	0.02
IndexPropertyDirectlyGte	third	88.89 ns	0.3116 ns	0.2915 ns	88.38 ns	89.34 ns	1.77	0.01
IndexPropertyDirectlyGt	third	89.82 ns	1.2134 ns	1.0757 ns	88.62 ns	92.23 ns	1.79	0.03
IndexPropertyDirectlyNeq	third	89.10 ns	0.4787 ns	0.4478 ns	88.33 ns	89.79 ns	1.77	0.02
LowerTrimSwitch	FIRST	41.28 ns	0.3438 ns	0.3216 ns	40.83 ns	41.80 ns	1.00	0.00
TrimEquals	FIRST	25.89 ns	0.2011 ns	0.1882 ns	25.64 ns	26.20 ns	0.63	0.01
IndexPropertyDirectlyGte	FIRST	30.52 ns	0.1330 ns	0.1179 ns	30.32 ns	30.74 ns	0.74	0.01
IndexPropertyDirectlyGt	FIRST	30.47 ns	0.2444 ns	0.2286 ns	30.19 ns	30.95 ns	0.74	0.01
IndexPropertyDirectlyNeq	FIRST	30.48 ns	0.1419 ns	0.1327 ns	30.20 ns	30.72 ns	0.74	0.01
LowerTrimSwitch	THIRD	48.24 ns	0.6442 ns	0.6026 ns	47.48 ns	49.52 ns	1.00	0.00
TrimEquals	THIRD	51.53 ns	0.1268 ns	0.1059 ns	51.33 ns	51.66 ns	1.07	0.01
IndexPropertyDirectlyGte	THIRD	79.13 ns	0.5426 ns	0.5075 ns	78.34 ns	80.23 ns	1.64	0.02
IndexPropertyDirectlyGt	THIRD	79.33 ns	0.6976 ns	0.6525 ns	78.82 ns	80.55 ns	1.64	0.02
IndexPropertyDirectlyNeq	THIRD	78.99 ns	0.5984 ns	0.5598 ns	78.25 ns	80.02 ns	1.64	0.02
LowerTrimSwitch	default	32.89 ns	0.1552 ns	0.1452 ns	32.71 ns	33.25 ns	1.00	0.00
TrimEquals	default	35.39 ns	0.1727 ns	0.1615 ns	35.15 ns	35.69 ns	1.08	0.01
IndexPropertyDirectlyGte	default	88.53 ns	0.4421 ns	0.4135 ns	87.70 ns	89.39 ns	2.69	0.02
IndexPropertyDirectlyGt	default	87.95 ns	0.1866 ns	0.1558 ns	87.54 ns	88.11 ns	2.67	0.01
IndexPropertyDirectlyNeq	default	88.01 ns	0.3978 ns	0.3526 ns	87.56 ns	88.87 ns	2.68	0.01
LowerTrimSwitch	first	27.68 ns	0.0585 ns	0.0488 ns	27.58 ns	27.74 ns	1.00	0.00
TrimEquals	first	15.19 ns	0.0832 ns	0.0738 ns	15.05 ns	15.35 ns	0.55	0.00
IndexPropertyDirectlyGte	first	30.63 ns	0.3207 ns	0.3000 ns	30.29 ns	31.23 ns	1.11	0.01
IndexPropertyDirectlyGt	first	30.59 ns	0.1283 ns	0.1138 ns	30.34 ns	30.75 ns	1.10	0.00
IndexPropertyDirectlyNeq	first	30.47 ns	0.1996 ns	0.1867 ns	30.12 ns	30.72 ns	1.10	0.01
LowerTrimSwitch	third	34.95 ns	0.1538 ns	0.1439 ns	34.73 ns	35.24 ns	1.00	0.00
TrimEquals	third	42.40 ns	0.1791 ns	0.1675 ns	42.06 ns	42.71 ns	1.21	0.01
IndexPropertyDirectlyGte	third	79.23 ns	0.3630 ns	0.3396 ns	78.53 ns	79.83 ns	2.27	0.01
IndexPropertyDirectlyGt	third	79.22 ns	0.3779 ns	0.3350 ns	78.57 ns	79.99 ns	2.27	0.01
IndexPropertyDirectlyNeq	third	79.38 ns	0.4484 ns	0.4194 ns	78.74 ns	80.10 ns	2.27	0.01