Okay so
Capcom, Sega, Konami and Microsoft.
You can UP their playable fighters to 6 reps. Who do you choose? Keep in mind existing reps count so unless you cut say Bayo you'd have 3 picks for Sega...
Capcom:
1. Mega Man (literally no reason to cut him)
2. Ryu (see Mega Man)
3. Ken (he's the original echo fighter)
4. Dante from the Devil May Cry series (I've effectively written five or six movesets for the guy, so I'm pretty passionate about the character)
5. Jill Valentine (tough call between her or Leon, but I figure a Resident Evil character should be in here)
6. Amaterasu (Okami's amazing - a stage in that art style alone would get me excited)
Sega:
1. Sonic (you'd have to be insane to cut him)
2. Dr. Eggman (tough call between Eggman, Tails, Knuckles, and Shadow - I could see Tails getting in as a semi-clone, or even a full fighter, but I think Eggman would have a more creative moveset)
3. Bayonetta (tempted to put Jeanne in here as an echo fighter, but then space would be limited.
4. Joker (since Joker was released, I've played through six different Persona games, if we're counting Persona 4 and Persona 4 Golden separately - the series is a lot of fun)
5. Blaze Fielding (from Streets of Rage; how do we not have a side-scrolling beat-em-up character in here?)
6. Kiryu (including the Majima Everywhere system! Open an item container? It's Majima! Use a Pokeball or assist trophy? It's Majima! Reach the boss at the end of arcade mode? It's Master Hand! ...Wait! BY GOD, IT'S MAJIMA WITH A STEEL CHAIR!)
Konami:
1. Snake (Snake? SNAAAAAAAAKE!)
2. Simon Belmont
3. Richter Belmont
4. Bomberman (it's a bit of a shame that he's just an assist trophy/Mii costume)
5. Goemon (don't know much about him, but he seems like he'd be fun)
6. Yugo (the main character of Bloody Roar, who can turn into a wolfman)
Microsoft:
1. Banjo-Kazooie
2. Steve
3. Master Chief (it almost feels like you've got to have him)
4. Doomguy (if Microsoft only included one green-armoured space marine, he'd be my choice)
5. Fulgore (I'm not sure who the main character of Killer Instinct would be, but Fulgore seems like the most prominent)
6. Joanna Dark (I probably could have included someone else instead, but I played through Perfect Dark for the first time not too long ago, and she seems like she could be a lot of fun)
I'm not sure if Microsoft's buy-out of Activision has gone through; if it has, then I might replace Joanna with Crash Bandicoot, but I'm not sure.