I used to be a big anime fan, but I'm not anymore, but I watched both series a little bit
from my own personal experience, I was actually able to watch naruto consistently for roughly 2 seasons without getting very bored (yes - after a while it gets boring in my view)
but, as for bleach, even watching one season was a chore for me - nothing kept me interested at all
but that's just my opinion and you should make your own judgement
I wouldn't recommend either of these animes personally; "good" shonen/saga animes I've watched would be berserk, rurouni kenshin (most of it; after 2/3 of it, it goes to ****), yu yu hakusho, trigun and of course dragon ball z (if you haven't already watched it) but I'm not much of a shonen anime person, or at least I wasn't; one piece is very slightly better than bleach and naruto is (in my very subjective viewpoint) better than one piece although as I've heard one piece doesn't get as boring as naruto does.
if you haven't already seen "golden boy", "great teacher onizuka" or "cromartie high school" (all dubbed versions) those are my favourites as they are hilarious