Well one piece has more variety imo, One piece can give pretty much any power to any person but they usually make it pretty entertaining whereas bleach it sword fighting with abilities that uses the sword, now i love samurai anime's but bleach just gets repetitive to me.
When it comes to filler onepiece is able to drop it in smother because most things end with them in the middle of the sea with nothing in sight so they can make them go anywhere and still make sense where bleach in example spends a lot of time in hueco mundo where making everyone go to the beach just doesn't fit at all.