Timing isEqual: and isEqualToString:

isequal.m

// clang -framework Foundation isequal.m
#include <mach/mach_time.h>
#include <stdint.h>
#include <stdio.h>
#import <Foundation/Foundation.h>

// Convert from mach time to seconds (gets set in main() below).
double ticksToNanos = 0;

// Run some code many times, timing how long it took, and announce the average 
// time.
#define Time(times, block) do { \
    uint64_t _start = mach_absolute_time(); \
    for (int _i = 0; _i < times; _i++) { \
        block; \
    } \
    uint64_t _end = mach_absolute_time(); \
    double _nanos = (_end - _start) * ticksToNanos; \
    printf("%60s %.2fns mean\n", #block, _nanos / times); \
} while (0)

int main(int argc, char *argv[])
{
    mach_timebase_info_data_t timebase;
    mach_timebase_info(&timebase);
    ticksToNanos = (double)timebase.numer / timebase.denom;

    // Some objects to be used in timings.
    NSString *interned1 = @"Ahoy there sailor!";
    NSString *interned2 = @"Can you do the otter dance?";
    NSMutableString *big = [[NSMutableString alloc] init];
    for (int i = 0; i < 100; i++) {
        [big appendString:@"I'm a pretty girl. "];
    }
    // Intentionally not a string, but we cast to avoid warning.
    NSString *array = (NSString *)[[NSArray alloc] init];

    const int times = 1e7;

    Time(times, [interned1 isEqualToString:interned2]);
    Time(times, [interned1 isEqual:interned2]);

    Time(times, [big isEqualToString:interned1]);
    Time(times, [big isEqual:interned1]);

    Time(times, [interned1 isEqualToString:array]);
    Time(times, [interned1 isEqual:array]);

    return 0;
}

Typical run on my machine, a late-2010 MacBook Air:

$ clang -framework Foundation isequal.m && ./a.out 
                   [interned1 isEqualToString:interned2] 153.39ns mean
                           [interned1 isEqual:interned2] 152.31ns mean
                         [big isEqualToString:interned1] 143.30ns mean
                                 [big isEqual:interned1] 143.04ns mean
                       [interned1 isEqualToString:array] 147.17ns mean
                               [interned1 isEqual:array] 124.43ns mean

isEqualToString: and isEqual: are neck-and-neck when comparing strings, though isEqual: always comes out ahead when comparing a string to a non-string.