For me, It would depend on how engrossed I am into the anime.
Rurouni Kenshin, Bleach, and Yu Yu Hakusho I watched from start to the last one currently.
To be honest. Bleach filler arcs have gotten really, really bad. The last time the Princess popped up I was wanting Bleach to end. The filler arcs that has that Princess in it is so lame.
Naruto, D. Gray Man, One Piece, and Inuyasha are ones that I have not gotten very far into before losing interest.
Some good ones have only 12 or 13 episodes.
Currently, I am watching Afro Samurai which far as I know has only 5 episodes.