I used a Valspar DTM primer/sealer and it was really good stuff. Sanded real nice and sprayed nice. I have not had any experience with other product except I did try so 5 Star primer and it was terrible compared to the Valspar. You can also tint the Valspar if need be. I went with white, which really made the color pop. I never thought it would have an effect on the overall look of the base coat but after doing some test pieces with different color primers , it is a factor.
It is holding up real nice. The SPI went down nice, with very little orange peel. Out in the sun it looks near perfect but when I get it in my garage with florescent lights you can see some peel and flaws from my handy work. I could cut and buff it but haven't bothered except I did do a few spots that got some dirt/nibs in the clear and they turned out fine.