First of all I tell you where NOT to start: Pokémon Mystery Dungeon: Gates to Infinity is just bad, I played the Demo and got bored, after that I watched the entire gameplay and I got even more disappointed, the game is short, too easy and lacks of a good plot that is one of the most immersive points in the game, at least for the games I played (Explorers of Time/Sky). I can't really give a proper opinion since I never got my hads on Red Team and Blue Team but the previously mentioned ones for the DS are some of the best Spin-off games I've ever played (keep in mind the person who's talking to you is a Pokémon fan so it might be very different for you ). From what I read Pokémon Super Mystery Dungeon introduces the Mega Evolution (somehow since there are no humans in the MD world and to activate this process you usually need a human, a pokémon, a megaring, a megastone and a bond between the first two) so it might be better to chose one of the older games first so that you get introduced to the MD mechanics/items and then you go ahead with even more mechanics as well as preventing any form of eventual spoiler from the newest titles regarding the old ones
