_Results.md

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.18363.836 (1909/November2018Update/19H2)
Intel Core i7-8850H CPU 2.60GHz (Coffee Lake), 1 CPU, 12 logical and 6 physical cores
.NET Core SDK=3.1.300-preview-015135
  [Host]     : .NET Core 3.1.4 (CoreCLR 4.700.20.20201, CoreFX 4.700.20.22101), X64 RyuJIT
  DefaultJob : .NET Core 3.1.4 (CoreCLR 4.700.20.20201, CoreFX 4.700.20.22101), X64 RyuJIT

Method	Mean	Error	StdDev	Gen 0	Gen 1	Gen 2	Allocated
Task_IsSynchronous	23.67 ns	1.356 ns	3.803 ns	0.0153	-	-	72 B
Task_IsAsynchronous	23.69 ns	0.507 ns	1.092 ns	0.0153	-	-	72 B
ValueTask_IsSynchronous	24.78 ns	0.500 ns	0.685 ns	-	-	-	-
ValueTask_IsAsynchronous	27.25 ns	0.559 ns	0.644 ns	-	-	-	-

Program.cs

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System;
using System.Threading.Tasks;

namespace ConsoleApp92
{
    class Program
    {
        static void Main(string[] args)
        {
            BenchmarkRunner.Run<Tests>();
        }
    }

    [MemoryDiagnoser]
    public class Tests
    {
        static bool AlwaysFalse() => false;

        [Benchmark]
        public async Task<int> Task_IsSynchronous()
        {
            if (AlwaysFalse())
            {
                await Task.Delay(0);
            }

            return 123;
        }

        [Benchmark]
        public async Task<int> Task_IsAsynchronous()
        {
            await Task.Delay(0);
            return 123;
        }

        [Benchmark]
        public async ValueTask<int> ValueTask_IsSynchronous()
        {
            if (AlwaysFalse())
            {
                await Task.Delay(0);
            }

            return 123;
        }

        [Benchmark]
        public async ValueTask<int> ValueTask_IsAsynchronous()
        {
            await Task.Delay(0);
            return 123;
        }
    }
}