PS3 joysticks have 4 pins on each axis instead of 3 pins like most joysticks. As far as I know, the PS3 joysticks can still be used for a Wii if you wire to the correct 3 pins. EDIT: Apparently some PS3 joysticks do have 3 pins. I'm not sure which you're wanting to use.
The sliders are probably the better choice because they are cheap, take up less space, are good quality, and people here k ow how to use them. I get that some people like the feeling of traditional joysticks better, and the PS3 ones will *probably* work, so it's really up to you.