In my opinion, there's really no "pokemon game that's best for beginners". Allow me to expand that.
Pokemon, as a franchise, has always been great for any RPG beginner. Nothing really "trumps" the other in terms of easiness/difficulty. Each title has a different story from the other, and consistently for 15 years, it still has retained it's very shallow learning curve. What I mean is that every title in it's name is easy enough for even children to understand.
Sure, there's EVs and IVs and whatnot. But those deeper stuff aren't required to beat the game at all.
Firstly, your goal is simply to save the world before bedtime be a Pokemon Master -- and with that said, you simply just have to collect 8 gym badges, kick a few bad guys' butts, and then enter the Pokemon League like a boss. In each gym, there would always be one NPC who would give you trainer tips that would help against fighting the said gym. In each game, there are even various signposts scattered throughout the maps with some valuable info.
Secondly, game over does not exist. You can re-do everything with only very little penalty (being a small loss in money). Got wiped out and forgot to save? No problem. Continue from the last Pokecenter and try again!
Third, there's always a way around. You are not prohibited from overleveling and the "bosses" aren't stupendously hard in such a way that you'd be forced to use specific pokemon, no. In fact, the game still gives you the fair chance to beat those powerful dragons without using ice pokemon at all! Additionally, TMs and HMs help a lot on making your team cover gaps you've missed. This allows you to avoid training a lv 5 pokemon to 70 from scratch just to beat one or two walls in the game.
Pokemon isn't hard at all. It always has had it's doors wide open for beginners and veterans alike. Just choose what gen/title you seem to like and play with it. There's absolutely no drawback.