I really like Mann Mansion. I usually play it while waiting to get onto the 2fort server. It's fun, but stalemates when you have good players on it. I'm not sure if you can set it up to spawn the HHHH without having an admin actually issue the command. I'd like to see it as an upcoming Halloween event alongside Harvest.
I'm with Hal on ZF. It really brings people to the server, and they are lots of fun. Prophunt is also hilariously fun. I would love to play either. Pyro dodgeball is fun, but not for long, so I might drop in, but wouldn't stay. EDIT: also, I <3 the official "events", like Mann Mansion and Degrute Keep.
ZF and PropHunt + alltalk = fun times for all. Yeah, Dodgeball is fun, but it gets pretty repetitive after a while. It's an excellent "in between" mod though, say if you were going from Zombie Fortress to PropHunt in one play session, dropping a Dodgeball map in between can be nice. Or even between maps of the same mode. So would I. And you're right, I think you need admin to spawn HHHH, which is really too bad. Running Halloween maps during Halloween is a great way to get people onto a server, too.