EA. They use a decent amount of IPs that they own, they make good games, and as a first party development studio, they might even bring back some of their older IPs. I couldn't see Activision or Ubisoft being first party because other than a lot of movie shovelware or imagine shovelware titles, they've only got two series they push out left and right.
If Square Enix was good like they were in the past, then I'd like to see them create their own console. Bandai already tried but it failed, so I'm sure they won't try again. If they made a console rather than a portable though, with how much the Japanese likes Gundam and Dragon Ball, they might be successful.
*edit*
EA and Namco would also have the most diverse first party games if they were to create their own consoles. EA would have racing, open world racing, action/adventure, military shooter, tps, wrpg, sports, and fighting(UFC/Fight Night.) Namco would have racing, action/adventure, tps, arcade shooter, jrpg, strategy, and fighting.
