Competitive: not relevant to how good a *game* is
Graphics: battles look the same yet XY can manage 3D in single battles
Handholding & Difficulty:
XY: optional gift pokemon, optional exp share, not that hard but most idiots say that despite using the exp share
SM: mandatory "no you can't go there, or there, or there" "do exactly what we say and we'll let you do more things", only more difficult because battles can go on forever which no one except lameos willing to spend all day grinding for the shiny bit to be 1 instead of 0 in a virtual animal
Region:
XY: Beautiful, lots of memorable areas e.g. pokeball factory, rich and poor castles, rock climbing, a better beach than SM, big circle city, windmill, some places in the overworld had 3D, had selfie cameras all over the region
SM: horrible, tarmac everywhere, garish colours, 2 tropical regions in a row, bad music, you have to hear HEEEYAMULADIERADAEH 1 million times, shitty camera that can almost never be used, gives you fake instagram friends who all love you because you're such a special child.
Rivals & friends:
XY: the one you compete with by battling, the one you compete with by pokedex, the one who fancies you, the one who doesn't care about pokemon
SM: the one who doesn't care about battling and chooses the weaker starter but still demands to battle you despite not caring at all, the one who's afraid of pokemon, the one who only shows up half way through and you can hardly ever fight.
Evil Team:
XY: Politically relevant, thematically fashionable and elitist, evil team leader twist reveal
SM: Lame, stereotype reliant, cut and pasted into the region, stupid idea that those guys actually took over a town and no one has gone after them, second evil team reveal was predictable because there was no other reason to spend so long there,
Legendaries:
XY: death bird, integral to the story
SM: wrong types, just randomly appear at the end
This is just off the top of my head.
