There are good custom maps, but there are also a lot of total ****. If you put all whitelisted maps on your server, then the list will be so huge, that map list loading, finding and choosing the map sometimes takes time longer than server timeout before auto-load next random map. Btw, is there some console command to vote for a map?
So I'm suggesting to put only good custom maps in server list. Here are maps I like:
Aventine (imo the best custom map ever build, hardcore gameplay, tough one, good visuals)
Chthon (great visual, but too easy)
Constriction
CornerMarket_v3 (small, very tough)
Crystal-LakeV1-7a (in memory of Jason Voorhees

)
Grimpen (beautiful marshland map, excelent visuals, but too big to be played by non-zerkers - up to 400m distance to trader)
HarbourV3
Swamp
TheLongDarkRoad (map is good both for zerking and camping, and also for camping as zerkers

)