I'm pretty sure in most cases, people enjoy the main series more. It's kinda hard to put spin-off's together in one category, because they usually branch into so many games that can be so different from each other, and while you may love some of them, you may also had others. That can be applied to main series games as well, but in cases like Pokemon (which is pretty much what most people are gonna use in this case since it's the most notable series of games which is split up into main games and spin-off's, at least for my knowledge), they're usually very alike, following the same concept, and mostly seperated by graphics, game mechanics and storyline, while a lot of the spin-off's are completely different. I prefer the main series games as a group, since there are quite a few spin-off's that I never really liked, which isn't the case with the main games.