With Valve, Half-Life and Portal seem to be their only good series' in my opinion. TF2 can only hold my interest for a few days, Counter Strike seems really boring, and DotA2 hasn't caught my interest one tiny bit. I despise Bungie and Blizzard. Nintendo has some good games. ICO has only made two games, and I haven't played either, but a little interested in them and will probably pick up the HD remakes... Naughty Dog is ok. Crash games were just ok and from the little I've played of Uncharted 2, I don't see what is so great about it... Would say Square Enix for the Final Fantasy games, but their other series' weren't too great. Same with Bethesda (Oblivion was just boring).
As for my favorite... hmm... People Can Fly and The Farm 51 and definitely up there, along with Irrational Games and id.