Depends on what you're looking for. If you're looking for competitive maps, check out the Featured Maps section. They typically don't choose mini-game or casual maps. Otherwise, it's all dependent on what you like. Personally I like infection, and Act 1 and Act 2 are some of my favorites, along with, not to sound full of myself, a couple of my maps that I made which have not yet been posted. If you're interested, you can add me on XBL. I host a Custom Games Night pretty regularly, and I invite any friends online. You could see some of the maps I use.
Your friends list is full, but add "walkerneo" if you get a chance. I made an infection escape map, but it's pretty lacking, so I'm working on another. Invite me to the next lobby you host please
Ah, that's right, my bad - I've got a bunch of people to delete who are never on. And so long as you're online, you'll get an invite.
This game is really fun for customs with 4-16 players. It's not really competetive but more for just fun, if that's what you're looking for. http://www.forgehub.com/forum/reach-gametypes/118855-dragon-ball-z.html
You can try my spider web map if you like snipers. Anyway i want to host some custom games tonight at 6:00 central if your down i hit u up with an invite. just go over to my post and post a reply.
Walk! My new buddy! Plasma's right, riftes L4D maps are pretty epic for customs. There was also this one minigame that got featured called club something.
Try quidditch 2, its a map I made, that I have had alot of praise for. The download links are in the video, and the video is right below this!! YouTube - Halo Reach - QUIDDTICH TWO!!