Like them both really, CoC is more challenging has you play the roll of both senior and junior officers. I think it rewards period tactics more so than BA too, at the end of the day they both give us enjoyable games which is what it is all about.
To be frank, Bolt Action is a better game imho but I will play CoC when Phil organises it. I dislike the fiddling with dice, patrol phases, jump off points and so on. Much prefer just to get stuck in to the game. That said, we only play CoC for WWI where I think it's a bit restrictive for the defenders in 1917-18 games. I've not used it for Burma or 1940 games in GHQ as we operate a 'My Toys, My Rules' policy between ourselves, so I choose BA.