Finally completed my living Alola Dex which is 403 Pokemon in the Ultra games. Looking at my Daily Records it taken me 91 hours in Ultra Moon, 34 hours in Sun and 31 hours in Moon to do it and using the GTS for a few of the Pokemon that either require to complete the game again like the exclusive UB or catching them in game is just a pain like Dratini. The Ultra versions are definitely the best made Pokemon games so far, everything loads quickly and there's plenty of Pokemon to catch. It also looks great with only occasional slowdown during 2x2 battles, I went back to X/Y briefly and its amazing how grainy those games look in comparison. it's just a shame the islands themselves don't change like the worlds do in other sequel / third games in generations so despite some story changes it does feel very samey and more like a finished version of the previous game than something new.
If you're looking for a first Pokemon game I'd definitely recommend the Alola games even when the Switch games come out because there is a lot to them and the first Pokemon games on new platforms are generally thin on content.