From snesorama.us:
Emulation for the Snes is close to perfect these days, and has been for quite some time. Both sound and video is running as smooth as the real thing, and you can even make it look better if you mess around with some settings on your emulator. In general a P2 or AMD K6 based system should be enough for good speed, aswell as Direct X of course...
Zsnes -
www.zsnes.com/
The best emulator available for the Snes console. Offers the widest game compatability, aswell as the lowest hardware requirement. The configuration of this emulator is also much better than with other emus, such as the Snes9x. Another FINE feature is the mousesupport which will come handy in games where you use a crosshair to shoot enemies, and similar games. I absolutely adore playing Tinstar (available at this site) using this mouse feature

The mouse doesn't require any special configuration, just hit the key mapped for the enabling of this option. Use the misc menu, for a list of available keys, and what they do.
Snes9x -
www.snes9x.com/
The 2nd best emulator for the Snes. At my previous sites I used to brag about it's neat little feature, which allowed u to play games 3dfx optimized

Although a cool feature, it's uneeded with today's computers, as 3dfx is dead

If u happen to have 3dfx (A.K.A Voodo), u'll be happy for this future. The emulator is otherwise very good with a decent system. In other words, with a new system, this emu will pretty much be just as good as Zsnes. I do however think that Zsnes is more convenient to configure, especially the controls.