Probably Valve, but really I don't hate any developer since I don't know anyone that works for any of them. Well, I hate Sonic Team, but that's just because I've always hated Sonic the Hedgehog...Maybe it's just Yuji Naka I don't like because his last two games (Let's Tap and Ivy the Kiwi?) have both looked like shit tacos with a side of vomit soup in my opinion.