Bleach started out quite strong but has been heading down steadily for a long time. I've actually stopped watching the anime because I couldn't stand it, though kept reading the manga.
Naruto has been up and down a bit, but mostly quite good. As far as the anime goes, it has the best fights by far, both in terms of animation/choreography and in thoughtful, intelligent maneuvering and interesting skills and the uses thereof.
One Piece, other than a few segments, has probably been the most consistently good. It blends humor into the show in a way the others don't, and achieves a level of lighthearted fun that makes it a simple joy to watch. Unfortunately, unlike Naruto who's filler tends to be of the 'non-canon story arc' variety which can be skipped or at least possesses a modicum of pacing, One Piece seems to be following the DBZ route of drawing out the main story as much as possible, which is making the current arc more than a little annoying/boring to watch.
In the end, I like (or have liked in the past and will like again when it catches up to the manga, in the case of bleach) all the shows. I voted One Piece, but Naruto is a close second. Suffice to say, though, that non of the big 3 will ever top my true anime favorites.