I would definitely stick with Dividend Miles. I have over a million miles on US and have had very few problems booking awards on US. However, I have 200,000 miles on Delta that I've never been able to use, unless I want to book a SkyChoice award for double the miles! I have never been able to book a SkySaver Award for the dates and destination that I want, even trying 10 months out. I've almost given up trying. But, whenever I'm booking an award, I always try Delta first just to see, and inevitably end up going to US and getting the dates that I want at the standard mileage rate.