X or Y they are easy enough. Also im asuming you are considering oras sense you are posting here. And you dont want to mess with ultra necrozma.

Depends if u want to revisit older titles tran ORAS are the games if u like story based with new mechanics,custom clothing and an easier experience then X&Y is the choice idk about (Ultra)Sun & Moon cuz i despise gen 7 haven't played tho so i might be hating for no reason.

x and y are too easy fun tho they give you your starter and a gen 1 starter at the start along with a mega lucario still great games and fun if your new i would go with ORAS on h shop theres a rom that beefs up everthing everyone is a higher level megas are used alot more