sony for me. i don't hate nintendo's legacy by any stretch, but i am not even lying when i say that, modern gaming is much more suited to my... tastes. i LOVE exploration, deep, deep exploration and big open worlds i can interact with and the sense of wonder that comes with exploring huge worlds in great detail, and while we're not quite at that, sony has the hardware more suited to offer me that.
(that's not to deny xenoblade chronicles x or anything, but IN GENERAL... xcx is an exception not the rule by far)
nintendo's older systems boasted harder gameplay, fwiw, but that's not my personal interest.
if i had to really choose, and let's pretend the vita is not the end of sony handhelds, i'd have to stick to sony. MORE jrpgs, MORE open world, MORE gameplay and sense of wonder suited to me.
playstation vs n64 is not a battle i was ever into, i thought both consoles looked terrible ngl. so i don't care either way.
playstation 2 stomps gamecube into the curb. the better tales game, way more jrpgs, way more open worlds, okami beats windwaker at its own game, plenty of platformers (r&c, j&d, psychonauts come to mind)... some of which (psychonauts, esp) i thought were better than sunshine. the gamecube had very little for me... except animal crossing. and that's where things get sad for me... no more animal crossing! DX
playstation 3 stomps wii for sure. wii had madworld and smg, but ahhh, not much else that interested me... playstation 3 has my biggest library, and will likely be my first system to reach 100 titles (tho the library is becoming 'scarce' for me, i think i can find another 35... i'm missing record of agarest war series, for instance)
and the playstation 4 destroys wii u.
psp vs ds was a lot harder for me, both were fantastic.
vita... ahhh, i think vita technically has less time for me, just because new leaf has sucked literally 300+ hours of my time from my life @.@ (compare to disgaea 3, which took ~100) but i prefer the vita overall, and have, iirc, more games for it. and that'll likely remain true to the very end. 3ds also has monster hunter these days. sighhh.
but yes, sony... ah, sony.
unfortunately, nintendo loses by a small margin in the handheld department often, but still.