Well, with Activision, they were in the development for Toy Story 2 and Buzz Lightyear of Star Command: Action Game. Both of these games made up a great portion of my childhood. In more recent history, I have really come to enjoy [Prototype] and would also like to look into the new Wolfenstein, as well as Ultimate Spiderman and Spiderman: Web of Shadows (seems like [Prototype] with Spiderman) and see if they're any good.
Electronic Arts... Well, they've made what I have found to be the absolute greatest 007 games I have ever played. GoldenEye (any of the three versions) cannot compare. I also really enjoyed Lego Island Extreme Stunts. I think it's the greatest Lego game I have ever played.
Ubisoft, I don't know quite as much about. I might have heard this wrong, or else someone might have been totally yanking my chain, but, I think I've heard something about Ubisoft dropping DRM. Again, I might be dead wrong about this. I'm glad that they finally decided to give another shot at good ol' Rayman again (Yahtzee sure seemed to like it)! I also admire what they've done with Assassins Creed. Not many other developers these days would go so out of their way to put in so much culture and historical accuracy at the level Ubisoft does.
I also like how all of these developers are big on PC. I've got a few PC games from all three of them, old and new. Also, Activision is "Friends of Dolphins". I'm not really sure if this is a good thing or a bad thing.
http://www.atariage.com/2600/archives/activision_patch_page.html?PatchName=Dolphin%20-%20Friends%20of%20the%20Dolphin&ImageName=Dolphin