Not talking about battle facilities as a whole. E.g. the other facilities in Emerald, as fun as they are, are irrelevant to the question. Only talking about classic Battle Tower or equivalent style facilities.

t. Emeraldfag here, never played beyond Gen 3, but want get back into Pogeymanz, but only really for Battle Tower style play, don't really care for the adventure part of the games, never really liked adventure games. I played the first 3 gen in spite of the adventure/RPG. I just like sports/fighting/general battling style games. So I want to know which games Gen 4 and beyond have the best Tower or equivalent, so I can catch up in knowledge to just that gen (all the new mons, moves, abilities, items), and then either find a completed ROM and build a team in there, or just power through the main adventure to get to the Tower.
Alternatively, if there's a ROMhack with a GOAT Battle Tower type facility, I'll go for that.