I have not had luck with versions past 2.6 until I loaded 2.7.2 Epsilon - WOW - the twitches are gone!
Even with default pids ( apm2, ublox, quad) flying was as smooth as can be. I did up Alt Hold P to .8 and thrust rate P to .6 because default let the copter sink when I turned on alt hold, but upping these values has fixed that - the hold is very responsive and will track terrain exactly.
I really liked 2.6 and ran many missions with good luck using it. I kept thinking that the next version would probably just have minor differeces. I was wrong - Jason and crew have raised the bar another order of magnitude!
For instance, here is a little 6 waypoint mission run several times under 2.6-
It hits all the waypoints and stays fairly close to the path. I thought this would be hard to improve, but now the same mission with 2.7.2 Epsilon-
Now it turns sharply and is amazing to watch - it is a robot with a real purpose now. The landing accuracy is almost scary. Watching it run at night as the leds streak across the sky is a rush.
One more round of applause for the team!