I love that this site gives version exclusives, because before playing a new game, I will often check it to see which Pokemon I'll need to trade for to complete the regional dex, but one thing that you also have to take into account when looking at which Pokemon to trade for, is Pokemon where you must choose over one or two other Pokemon who then become unobtainable.
Premium examples of this are starters, fossils in most games and Hitmonlee and Hitmonchan in gen 1. I understand that this information can't be obtained as early as version exclusives, but I would still like to know which Pokemon I need to trade for that aren't version exclusive. Thank you.