Project64 has the best compatibility with the games.
1964 has a great compatibility too, but the sound is sometimes skipping and the loading-times between the levels are sometimes extremely long.
UltraHLE is fast but the problem is the compatibility.
Corn does support only about 200 games (very much doesn't run fully), and much supported games hasn't got sound on corn. But corn is an extremely fast emulator, and some games are running on a p 200 at full speed! I've seen corn running super-mario 64 on a PII 350 mhz at screen-resolution 1280x960 with sound at full speed.
Project64 is the best one of all the emulators but some times slow. A high end is strongly recommended! At least a 600 mhz with 128 mb ram and 16 mb video (to run small games like mario64, mario kart and bomberman at 640x480). For more heavy games like zelda, super smash bros and perfect dark 800 mhz or more is strongly recommended!!!