otterbox defender is by far the best case. i have had one on my hero for several months and i love it. i am a cabletv installer and as such i am pretty rough on cell phones and cell phone cases. my hero has no scratches, drop marks or any other damage for that matter. i have accidently pulled it from the hip holster, while i was 30 feet in the air hanging from the cable strand, and it almost hit every rung of the ladder for the first 20 feet or so then feel the rest of the way to a concrete driveway. no damage. i don't recommend that you try this on your own but its good to know that it can take it if you ever do. my phone still looks "just out of the box" brand new.
the case does, however, literally double the phones physical size.
the only con that i MAY have noticed, is that a very few and select group of people that i talk to say that there is an echo on the phone with the case on it. (they always say, "you have your phone in that otterbox don't you?" well of course i do. it is ALWAYS in the case. one of these days im going to take it off and see if they notice.)
EDIT: it was always sounded fine on my end.... so they will just have to deal with it. lol