I have used P3, GW, Armory, Duplicolor, Board to Pieces, Krylon and Rustoleium.
Avoid GW, it's way too expensive
Avoid Armory, i have used two cans of it and they were both bad. The paint came out flaky and made the mini fuzzy from BOTH cans.
Board to Pieces was alright but about 2/3 of the way through the can the spray started splattering and not going on evently and even a soak of the nozzle in paint thinner couldn't fix it.
Krylon and Rustoleim were both ok, i didn't purchase them they were my LGS's "here you can use this primer" cans
I am currently on my first can of P3, i'm using their white primer. it goes on fairly smooth, a bit thin in some spots but it think a change of angle of the can will help since it has the nice flat stream, if you try and spray it right at the model you aren't actually spraying right at the model but above it. you need to cock the can down a bit to get it aimed right. i like it quite a bit
Duplicolor has been the best quality for the price. can't beat $3-5 a can.