Mine is surf
Prison break servers are extremely hard to populate and considering the fact that we struggle to populate our current servers I probs wouldn't bother putting one up till we have a lot of players who play on our servers. Deathrun servers are hard to populate as well and I don't like classic source servers

especially since the update just changed all the weapons recoils

. Best bet is a minigame server since they are very popular and tend to be a bit easier to populate; Plus there are loads of good maps for minigame servers. Zombie servers are also a good choice because people enjoy them

so you might wanna keep that in mind.