I definitely feel the love hate relationship with pokemon... I feel like the mainline games sometimes are quite a bit boring and really wish they would explore more of the side games *cough* mystery dungeon but most of the times, I like it!i would say pokemon is my favorite. although i have a bit of a hate and love relationship with it sometimes. i do enjoy most pokemon games i just wish it wasn't so cash grabby at times. then it would be fire emblem and then animal crossing.
I still have my little light attachment for my GBC! And it still works! Ahh, man, Gen 1-3 hits the nostalgia so hard. <3Didn't even have to think about it, by far Pokemon! Grew up watching my sister play gen 1 on her Gameboy color, with her little light attachment. Played consistently since gen 3. I'll admit I might have to give it a nostalgia run for the earlier gens since I was kinda young and not even knowing what the story was about lol but the pokemon aspect I absolutely love
I would say Smash is a close first as well, just that I never play that game alone and only ever with friends (and barely at that, now)