I think Dragon Tail's lack of STAB probably makes it a B/C grade move. Heavy Slam looks decent.
I got lucky with Iron Tail/ EarthQuake but then my Scizor got BP.NightSlash and I think NightSlash probably makes him second rate.
It's still a bit of a guessing game though. until lots of battle simulations have been run we can only really go on DPS/EPS and that can be misleading.