I'd say One Piece is a much better option. It's really long but worth it in the end.
The thing about Bleach is that it does start off really good. A bit cliche, but as a story it's still not bad and the development is very good.........for a while. But after the Soul Society arc Bleach slowly but surely starts to derail and before you know it, it becomes a mindless action series with awful character development and obvious plot no jutsu. Bleach has a good start but it dies out as it progresses and in my opinion it was bad enough to ruin the whole experience for me.
OP starts off a bit slower than Bleach, but once it gets going, it really gets going. Arlong arc is where you really start to see the awesomeness build up, and Alabasta on is just fantastic. One Piece is certainly one of the best Shounens I've ever come across with fantastic action, great character development, and so many deeper issues that Bleach would never even touch on.