DM7. Can't reccomend them enough. Not so much the DM8/9 (had a DM8, never worked, teammate's DM9 is downright terrible).
As long you take the time to clean the bolt engine after every day's worth of play, understand when to replace O-rings and don't mind putting a battery in it every month, it will just.....work. Stick a Steelie (3000 psi air system) and a Halo on it, it may not be the lightest of markers, but the only real weak point will be battery life.