Atlus. Persona 5 outselling FF15 would be epic!

Marvelous... they publish great games but Nintendo would do a better job at advertising & selling games..

Definitely. They consistently  makegreat games, but no one can play them. Nintendo taking the publisher role would OWN.

But to choose a company from the list above, I would say Capcom. If Nintend bought Capcom it would be game over. I'm pretty sure close to every genre known to man would be covered. A lot of money would be lost on exclusivity though.

I would like them to buy square

I tend to think that the only company that actually makes much sense is Marvelous because:

1. They tend to make good, overlooked, games and aren't afraid of taking risks like the hyper-conservative NCL.

2. They'd be super cheap to purchase due to recent difficulties since Nintendo likes to squeeze every yen until it screams.

3. Being relatively Nintendo-centric would create much greater synergy since they wouldn't have all the wasted technology and overhead and IP that just about all of these other huge (in comparison to Marvelous) companies do being so heavily invested in HD and multi-platform development ensuring that a large percentage of Nintendo's investment would be wasted money.

4. Buying someone (like S-E, for example) would almost be a strategic decision to deny certain IP to Sony and MS, but that's a fool's errand, long-term, when Nintendo can build their own IPs like Last Story and Xenoblade (and more ten times over and beyond) for a fraction of the cost.

So, yeah, my vote, such as it is, would go to Marvelous since they're the only deal that's reasonably on the table at the moment that wouldn't cost billions with a lot less jobs lost/wasted tech/etc. and they actually, to some degree, have the potential to shore up some of Nintendo's weaknesses, particularly given access to reasonable marketing budgets.