With exception of obvious diplo maps, where every territory is a bonus, I would recommend:
https://www.warlight.net/Map/19814-Twelve-CitiesLots of scenario possibilities, support diplos from 12 to 40 players very well.
https://www.warlight.net/Map/9071-Land-KaladorIdeal for fantasy diplos. High variety of super and mega bonuses supports scenario making, different races included already.
https://www.warlight.net/Map/6496-Issanders-Huge-WorldVery suitable for real world diplomacy. You can fit many players and make very balanced custom distributions.
https://www.warlight.net/Map/19653-World-NoliterreGood for both diplos and big team battles. There is series of diplos ongoing on this map, too:
http://noliterre.boards.net/https://www.warlight.net/Map/17567-Thirty-Years-War-16181648Very usable for all kinds of historical diplos taking place in Europe.
https://www.warlight.net/Map/18383-Orbis-Veteribus-NotusMany possibilities for scenarios regarding ancient and early medieval world.
Edited 9/19/2017 17:56:46