1. Nintendo - Grew up on them and they still hold some of my favorite franchises
2. Valve - Portal and Left 4 Dead nuff said
3. Bethesda - Elder Scrolls (And I'm not band-wagon, I've been playing since Morrowind, which is more than I can say for some many...)
4. Namco Bandai - Between the Naruto Ninja Storm series and the Tales JRPG games (Tales of Vesperia ftw), I love them
5. Ubisoft - Assassin's Creed nuff said
P.S. - I would say Square Enix buuutttt... MAKE KINGDOM HEARTS 3 ALREADY AND STOP MAKING DS TITLES!!!
I love Nintendo for their originality and how they can squeeze so much out of a their consoles even to the end of that console's lifetime. I also like SEGA and what Rareware was when they made N64 titles.