Alright. Let's make that specific question for you. What new purchase makes the most sense iyo? (Discounting Captain_Yuri b/c that's already assumed)
Hmm. I don't see much point investing in the Japanese market unless you go much further than just buying one company, so that largely eliminates Japanese companies. They do have some valuable franchises, but off the top of my head, I can't really name any that I would expect to make a huge difference. I'll go with EA for the sports titles, because exclusive sports titles would probably be pretty big in the long run. Of course that's assuming MS would make them exclusive, because it doesn't seem guaranteed (looking at Minecraft and Zenimax here). For what I imagine to be a more affordable acquisition, Blizzard might also be a good choice, althoug the PC focus of WoW eats away some of the benefits. Sega and Ubisoft would also be good for gaining a bit of strength here and there, but my overall choice is still EA mainly for the sports titles.
Of course that's all ignoring costs... EA is huge and might not be either practical or even feasible (although more likely it is feasible).