Below are my picks:

Microsoft

High Voltage Software, Insomniac, Epic Games

Sony

Platinum Games, Q Games, Sucker Punch, Quantic Dream

Nintendo

Next Level Games, Silicon Knights, That Game Company

What developers do you want/think each of the 3 should buy?

Definately Quantic Dream for Sony!

Microsoft - Epic Games

Sony - Square Enix

Sony - Atlus

No-one else is worth buying from a practical point of view as they won't be worth the amount paid.

Microsoft would not buy none of the 3 dev's that you listed especially Insomniac since they are just now starting there multiplat status.

Sony best option at of that list would be Sucker Punch. Quanitc Dream is a Private developer so i dont think they could get them. And Platinum is with Sega so thats not even possible.

Nintendo best option would be Next Level Games. That Game Company has not even made a single game for Nintendo so getting them would not make any since. And Silicon knight has not made a game for the Wii this gen so getting them would also not make any sense.

The Big 3 should buy nobody .... Lets try keep some form of independence because these smaller developers ar whats gonna keep the creativity alive. Other than just being fanbois who just what to make sure all there favorite games only appear on thier Console choice I cant fathom why everytime a aspiring Developer comes along you want them to bought .... there are disadvantages to being bought you lose alot of creative freedom ... and usually get stuck workin on what made you popular .... or you just be destroyed like Rare.

I don't know about the other two, but Sony should have really purchased Insomniac. And definitely Quantic Dream.

If Sony were to buy SE I think it could help them get our of their slump. SE games aren't bad at all but they are making some stupid financial moves.

Btw lets stop dreaming a be real... if Insomniac is gonna be bought by anybody it will %110 be Sony. Hell...Sony in since owns Insomniac already. Edit HVS!!??? that whack ass company thats been manly Nintendo??? why would MS want anything to do with them. again if anybody was gonna purchase HVS it would Nintendo... but I doubt Nintendo wants them either.

Square has always made bad financial decisions, remember Squaresoft and how they got almost bankrupt not one but two times?

What you mean is development processes rather than financial moves.

Anyway thats besides the point.....its not practical buying SE, they cost too much and the dividends for SONY wouldn't be enough, remember now SE includes Eidos, they will cost too much.