I have been told that the best one to get is the adaptoid but its near impossible to get and when they are on eBay, etc, they can be extremely expensive.
if you can find one called an "adaptoid" buy it. They have rumble and memory cardsupport and are much better made than that crappy n64/psx adaptor. However the adaptoid is kind of expensive because it stoped being made in 2002 and people dont really like to part with them.
THe real adaptoid is black and only supports n64 controllers. but if you cant find one the cheep $10 adapters arnt bad. they just dont support rumble and such.