flood is great because of modding and the fun variants that have already come into the community through that.
like SMASHY CHASE!!! woohoo, shameless self-promo plug.
besides flood, i love playing CTF in customs. you almost always have a great game.
Well for a more casual play, and maybe with less people (like 4 split screen) Slayer or Regicide is best. But with larger groups it could be more fun to do CTF or KoTH
I enjoyed KOTH alot on matchmaking while they had it!! Still fun on customs. Flood can be fun sometimes. Regicide is great. I like that its free for all with the twist of adding a king to it!