Bottom line on servers: Use maps that fit the slots you offer. If you have 50 slots, do not use maps that are crowded, arty infested, or poor performance wise. Basovka is one example that is perfect at 32 but by 44+ is murder. If you run 24 slot servers, don't run large scale maps like Berezina.
Be smart. Match the slot count to the maps and what they offer. Map selection is key and look for maps that offer the most dynamic play which leads to higher replay value. People get less bored.
Personally, I prefer mid to large size CA maps where everyone has something to do. I still find Kessel to be one of the single best infantry maps made. Tcherkassy is very high on my list as well. I also think the more players the better but mappers need to consider this when building and setting up roles. Give people something to do and craft the load outs accordingly to offer the most and prevent the most abuse.