Wait, what? Didn't you just say it was Ultra Moon in another topic? XD Anyway...um, the only one I've played is X, but I like X a lot for what it is. I haven't touched Gen 7 myself (Why didn't I get UM again?)
I think the ORAS games were the best for the 3DS. SM and USUM were just bad imo. Also, the only thing I really liked in XY is mega evolution. Hopefully Gamefreak doesn't try to pretend it never happened again on the Switch.
I really liked Y. I know a lot of people didn't, apparently, but I really did. It's probably one of my favorite generations.
I like ORAS mostly because of nostalgia. I'm not saying the other games are bad, but I feel like they just aren't as good as the previous generations.
ORAS! Sapphire was my first Pokémon game, so as you can imagine I was stoked to be traveling once again through the Hoenn region. I know some fans were a bit mixed on ORAS, but I personally loved it, and it definitely lived up to my expectations. It also introduced some of my favourite mega Pokémon. Mega Lopunny, Mega Altaria, Mega Pidgeot, Mega Sharpedo, and Mega Rayquaza just to name a few. I highly enjoyed Sun and Moon as well, although it did feel a bit slow and easy at times. The awesome new Pokémon and interesting region made up for that though.
Alpha Sapphire was my favorite. Even though there was no character customization, the character designs already looked good. The different features they had (like the showcases and the Secret Bases) really added on to this game. Also, how you can get so many Legendaries and fly around the region! It was a really enjoyable experience for me, and also a pretty good challenge. I hope another game like this one is made.
I think regular Moon was my favorite, I spent the most amount of hours with it as well lol. I just loved how smooth the gameplay was when I started playing and I had lots of fun post game filling up the Dex and doing several hunts/challenges.
X & Y were my favorites simply because they inspired me to travel to France. Also, almost all the Pokémon introduced in that generation were amazing and useful.
In terms of gameplay I would say Omega Ruby (and by extension, Alpha Sapphire). It had a lot of features such as Secret Bases and the second Day Care facility in the Battle Resort that just made it a more worthwhile experience for me and managed to keep me engaged long after finishing the story (plus the Delta Episode, which meant there was more to the story). In terms of story I would say Sun (and by extension, Moon). I felt that the story was probably the best in the series so far and a lot of the characters were very memorable. However, the games made a lot mistakes in terms of gameplay, which is why I still consider OmegaRuby/AlphaSapphire to be better in that area. There isn't really much to do after finishing the story, it isn't as easy to grind in the endgame/postgame, the Day Care was replaced with the Nursery (one of the characters says that it's less expensive, when its actually the opposite), and the relative lack of multi-battles.
If you count the VC releases as 3DS games, then definitely Crystal. Otherwise, I'd have to say Omega Ruby.
Definitely X and Y. They were the first games that I invested hours upon hours into. Kalos had some incredible music, in my opinion. It was also the first game to introduce the new-and-improved Exp. Share, which allowed me to train more than six Pokémon for my team for the first time.
XY are my faves. Than smusum. Are fun games Sahpire and ruby are my least cause somehow I couldbt get into it I did miss thw characterr customaztion there
Given my love of gen3, of course ORAS are my favorites. I'm actually such a big fan of the Delta episode too, they managed to layer the story between XY and ORAS in an impressive way, and gave the game a lot of depth that I thought XY was missing.
Moon. In my opinion, SM had the second best story of any pokémon game (after B/W), and I love the night theme.
