Most of us at the shop have Diving Concepts because that's what the shop sells. One of our guys has a DUI that he's had for a few years now. To be honest with you I don't think you will go wrong with either one. Its more a question of which options you want to go with. Since each has a few differences, those options and the price should settle it for you pretty well.
For me the integrated boots on the DC became a problem with wear on the soles, after only two years. Someone said the boots had been changed, but I haven't seen one recently to be able to tell the difference. I had socks put on mine, and bought some DUI rock boots, go figure. Its a little more hassile putting the suit on and off, but the boots are much nicer than what came with the suit originally.
The zipper on the DC looked to be a better zipper, but that may be an older DUI and they may have a better zipper.
One thing I do know is that all of the people who got the front entry don't like it much. The couple of us with a back zipper love it.
I have the Pro 650 HD suit, and the material does seem to be very durable, but not much flex. If I had to do it again I would go with the UltraFlex, the couple of people with it really like it.