@Savi:
I'm genuinely surprised.. How can you have read Prince of Tennis, the whole 42 volumes of it if you considered it the worst manga you have ever read? I man surely you would have just stopped after say 1-2 volumes if you didn't like it, I just don't understand why you are saying the ending is bad, is a very 'normal' ending..
As for best last arcs, too many last arcs take waaaaaaaaaaaaaay too much time, recent examples include BLEACH and Naruto, because the author tries to resolve as much as he/she can before finishing, and if JUMP doesn't cancel it like with Shaman King or Saint Seiya some authors have over extended their manga too much.
E.g. Dragon Quest Dai No Daiboken, sure the ending was fun and everything but IIRC the last arc starts at like volume 23 or something and this manga is like 38 volumes long (If my memory is right, I read it like 10 years ago lol) I remember thinking, how is this gonna continue for 15 more volumes? (I knew it was 38 volumes long) the answer is the authors dragged it and pulled characters out of their asses, like really new characters appeared out of nowhere.
I guess my favorite JUMP could be Slam Dunk, the last match was perfect, I remember how I read the last match from start to finish in a single sitting, and the last couple of chapters I was pretty damn excited.
Other good endings would be Yu Yu Hakusho if you consider Black Chapter to be the last arc, and if HxH had finished in the election/Alluka arc that would have been a great ending too.