i can't really decide which one is best, because everyone has specific things... and even if someone doesnt like somewhat more cartoony appereance of Guybrush in Curse of MI, its the first one that introduced Dominic, and brought already great writings to new level. Also, Monkey 1 has genuine naive, bumbling Guybrush, who thinks he has everything to be a pirate, who thinks he is irrestisable lover.. Monkey 2 continued in that style, with great humour and style. As for Monkey 4, even if graphic is not perfect and has control problems, i think old Guybrush is there with some great jokes. One of the funny moments is when he is talking to girls, as for example when he changes voice - "Why hello there, Brittany"
As for the worst, it was really obvious.