I have a Dillon 650 and have used Titegroup, Unique and Power Pistol for my 9mm.
I find that the Unique is harder to keep an accurate weight because of the flakiness of the powder. But I know some people love it because it is a very versatile powder and can be used for many calibers.
I like the low weight needed of the Titegroup, since I can reload a lot with one bottle, but there's a greater chance of over charging the case too...
Power Pistol uses a little more powder, but is easier to measure, and because of that, it's my favorite powder.
I'd use any of the three, and am scared to try others since im sure they'd be fine too, but I'd rather stick to one handgun powder and Power Pistol is my choice.