Personally i'd say XY and gen 6 in general, mega evolutions are excellent and they made an actual effort putting lore into the games (plus i'm french so i may be biased because kalos), ORAS were imo the best remakes ever and are exactly what a remake should aim to be.
Gen 5 is my absolute favorite out of them all . I love the plot of this game and also like how it forces you to play with unova's own pokemons until you have the national dex , which is fun since I won't be using the same pokemons I always use and will try something new .
Also I really have a soft spot for gen 4 , imo it has the best soundtrack of them all .( I personally love the nighttime pokecenter theme and distorted world theme )
Johto was also really good , I like the region's history . Wished Gen2 had a bigger plot (or a plot at all lol).
3 is probably my favorite, too, and the one I played the most as a kid. I stopped paying attention to Pokemon for a while and missed when the remakes came out. I played them a few months ago and really loved all the content they added. I went in blind and was blown away.
I probably need to go back and replay to make a more objective opinion, but I remember the feeling of Gen 2 with the day/night cycle, breeding and baby Pokémon, and then when Pokémon Crystal came out with animated sprites during battle. Definitely my favorite.