ZSNES has kind of terrible sound emulation. It's even worse in the netplay versions. That said, ZSNES is the only emulator with viable netplay. Note that the word there is viable, not reliable, not good.

SNES9x is more accurate than ZSNES, but the netplay doesn't really work. I've even tried it on lan and it's still terribly desynced when it works at all. It eats a little bit more resources than ZSNES, but on a modern computer that shouldn't be an issue at all.

As mentioned above, BSNES is the best in terms of accuracy, but the UI is cryptic, and it takes a powerful computer. I'm running a 3 GHz dual core, with a decent video card, and I get major slowdown when I try to play it.