Seeing how Nintendo treated monolith, I want them to buy over Atlus. I am sure Nintendo will mostly let them do what they want.
If not then Sony, but I cannot imagine them buying over all the ips and treat them right. Do not think they will want another tlg in the form of persona 5 again...
You mean how Monolith has written the safest plots in it's history under Nintendo, or how it took a fan campaign for Nintendo to even bring their best game out in the U.S.?
If Nintendo buys Atlus all their games will be region locked and we'll be lucky if even the biggest franchises make it outside Japan. That alone is enough of a reason to want Nintendo to stay the fuck away.
Sony meanwhile is region free and while they haven't localized all their titles they are at least willing to let someone else do it if they won't.
Imagine if Sony buys Atlus and SMT/Persona singlehandedly revitalize the Vita.
Imagine if Nintendo buys Atlus and SMT/Persona singlehandedly revitalize the Wii U.
Have you checked to see how SMT/Persona sells? They aren't system saviors on a global scale by any means and are only a middling system seller in Japan.
Exclusive access to Atlus' library would likely boost Vita just enough to make it a viable second handheld behind 3DS in Japan and Japan alone, getting them at least a look from most 3rd parties. That would largely only happen because Atlus is already up to speed on the PSV with multiple releases out and coming soon, and the assets for a PS3 release of P5 could quickly be transitioned over to a PSV release instead (or go cross platform to maximize sales). They would have to completely retool for Wii U development and the problems they've been having with HD consoles (hence the delay of P5) isn't exactly something Nintendo can step in and fix since they're having the same problems. Waiting 2-3 more years for P5 on Wii U isn't going to help the Wii U much at all.
If any of the major first parties bought them it would make the most sense and have the best results if it was Sony. I'd much rather see GungHo buy them and begin to expand themselves into a more relevant 3rd party company myself, but I'm not sure how well Atlus' business (tied heavily to physical distribution of titles) ties in with GungHo's mostly digital distro success. It's very possible GungHo would view Atlus' distribution and localization arms as meaningless, making an acceptable price point for their purchase pretty unlikely.