I only have the HC1, having used the bulkier FX1 until lately.
So Im biased if I say even the HC1 is not large.
Saying that , the HC3 is positively dainty ( easy on the hand but may be more prone to shake), seems more point/shoot user friendly , Outputs direct to HDMI ( an advantage if your display doesnt like HD signals via component) .and meaning you dont need to cable in audio separately
I must say I find the HC1s low light perfomance acceptable and Im sure those who say the HC3 is better are right although Im yet to see a "prosumer " camcorder with the Sony Vx 2100s excellent low light abilities
I stumbled accross
This thread from another forum on the same subject
Simply put ;looks like the HC3 seems better for you ( and less costly!)