Check out some videos from ETA Prime or Retro Game Corps on YouTube, I have many of them, favorite being the RG551V at the moment. Waiting for the Odin to arrive, I think that will be the one the plays most systems quite good, up to GC, PS2 and Wii.
You could also go for the RG552, but that price difference between that one and the Odin is very small, I'd than rather get the Odin.
Depends also which games you wanna play, if DC, N64, NDS and PSP are needed, you obviously have to pay more.