You should pick an emulator depending on what do you want from it:
1. Higan/bsnes - the best
- the most accurate emulation
- emulate pretty much all of available SNES hardware
2. no$sns - the paradise for the hacker
- PPU (VRAM) Viewer (screen, BGs, Tiles, Sprites, Palettes);
- I/O viewer - you can see PPU, SPU, DMA/HDMA registers
- Debugger - trace, breakpoints (the best Debugger I have seen for SNES)
- neat features - Assembly/Disassembly on the fly, Assembly in memory
- other features - that I have never used: BSS/NSS tokens,...
3. ZSNES - save-state donor for many tools
- fast emulation - good for old computers
- Net play
So if you going to hack, 2) is a must (if you want easy life that is), 1) is needed if you write ASM code, 3) if you use tools that can use save-states.