With exception of obvious diplo maps, where every territory is a bonus, I would recommend: https://www.warlight.net/Map/19814-Twelve-Cities
Lots of scenario possibilities, support diplos from 12 to 40 players very well.https://www.warlight.net/Map/9071-Land-Kalador
Ideal 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-World
Very suitable for real world diplomacy. You can fit many players and make very balanced custom distributions.https://www.warlight.net/Map/19653-World-Noliterre
Good 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-16181648
Very usable for all kinds of historical diplos taking place in Europe.https://www.warlight.net/Map/18383-Orbis-Veteribus-Notus
Many possibilities for scenarios regarding ancient and early medieval world.
Edited 9/19/2017 17:56:46