As bandg said, scopes are very subjective! I own lots of Vortex scopes from the Crossfire and Diamondback up to the Razor & Golden Eagle and absolutely love them. I know lots of people like their Hawke scopes, I am not a fan of them at all. I also think there are just too many better options available for the same or less money these days.
I'm not sure which Diamondback you're considering but I absolutely love the Vortex Diamondback Tactical FFP. I got mine when they were first released, on sale for $284 but even at $349-$399, they're a great deal. The turrets are great, they track perfectly, they have a great magnification range, they're crystal clear/sharp, I love the reticle and they have a lifetime warranty. I'm sure some will complain about the reticle size, as it is a FFP. But that's how it goes...Some complain when they're too big, some complain when they're too small. It's a great scope for the money!
Stoti