Most will say Red's. Supposedly his coupler that joins the two pumps together is a little less restrictive than ATR's. I have the ATR setup in my car and it was a drop in no brainer install. Also the ATR setup comes with a second pump indicator light which from what I am told Red's doesn't. Can't go wrong with either IMHO.
I like ATR's....comes with a new bracket (you have to send your old bracket to Red ) all the new wiring comes with ATRs also... I have also used both ...
Reds - Top quality, excellent to deal with and top notch customer service.
ATR - The quality may be ok but they have the absolute worst customer service. If you have any problem with it, it will definetly be how you installed it or something else you did wrong.