The new Diamondback HP line is quite a bit more expensive than the old trusty regular diamondback line. The 3-12x is actually the same price as the viper 4-12x, which is a decent hunting scope. I haven't looked through the new line, and haven't yet read any remarks on it, it's probably an unknown at this point. I'm assuming they have done some coating upgrades to incurr that much if a price hike.
For the same $400, you could look at Burris Mtac 3.5-10x or 4.5-14x, the latter is on close out pricing at most Sportsman's warehouses and is mil/mil.
Also, Vortex Viper PA 6.5-20x and HS 6-24x are around on sale under $400 and are known decent glass options. I have actually come to like Vortex's dead hold bdc reticle for some things and find it more useful than the vplex.
Other options I'd do before the new diamond back, IMO are: Leupold Mk AR 3-9x and 4-12x
And, the Weaver Tac 3-10x40 from Midwayusa (probably the best value in a sub $400 optic out there).