Delta miles are nearly impossible to use!
I have at least 4 trips already planned for the next 12 months and couldn't get award tickets on any of them unless I was willing to make multiple connections, take all day to fly and fly on regional jets for very long distances. Junk! With AA I can nearly always get non-stops on full size airplanes!
Also I have one Delta award certificate that I've been unable to use. I don't recommend switching miles to Delta.