Everyone I've talked to with experience recommends the D4. Haven't had a reason to explore this fully myself as my band has been focused on recording our album rather than playing live.
I have the DM5. It's ok for live use. I think D4 has better samples though. What I have heard is that D4 has random latency. So it can be a bit tricky to mix it with acoustic kick because of the phase problems. DM5 doesn't have this problem.