I would start now because you don't know how long they may drag it out, especially since they have fillers like every five-ten episodes and two entire seasons are filler!
When ever you start watching, you can skip all episodes involving the Bount, soccer, a princess, and a new captain for 5th, and not miss anything important or interesting! >_< I would say 100 of the 300 episodes are all filler! You can also skip through much of the dialog between enemies during battles as they mostly talk about their power, resolve, or emo past.
Kid Izzy-Chan
I want to start Bleach since my brother talks about all the time. However, I'm unsure if I want to start it now or when it finishes since there are over 300 episodes.