for me mario sunshine is definitley the weakest in the series! can't quite put my finger on it but i never bothered trying to get pass the second level (un heard of for me as ive completed all of the mario series apart from galaxy so far)
mario64 took me alot of getting into to start with but once i got the ds version i loved it
i still think the 2d versions are the best with my favourites listed in this order!
supermario land (snes)
supermario bro3 (allstar version snes)
supermario bro (nes)
mario galaxy (wii)
supermario bro2 (nes)
supermario sunshine (cube)
counting other mario games
paper mario the thousand year door (cube) has got to be my favourite game of all time