I cant provide a lot of input because ive mainly only used PPG bases. Ive been using them since I started, and theyve always performed well. Even when I was learning, and unknowingly did lots of things wrong, i have never had any issues. I generally use their mid grade base which is the omni plus or shopline plus. Ive experienced good coverage, smooth application and good matches using prime variants. Ill only use the deltron line if a color isnt available in plus. Sometimes ive had better matches in plus versus deltron on the same color.
Im not a ppg spokesperson and im not a pro painter, and im sure there are much better products on the market but im just sharing what ive have good luck with.
On another note, I worked for a automotive salvage company years back that also occasionally rebuilt cars. I wasnt the painter there but the painter used a lot of Nason because it was cheap and we generally built cheaper cars. But I was never impressed with the Nason line of bases.
Another note concerning coverage, i usually use tinted sealers prior to base to acheive coverage easier. That way I use less base because sealer is a lot cheaper than base. By doing this; A lot of times on a standard color, (white, black, etc) with the exception of metallics and pearls of course, i can get a way with only one coat of base. Less work for me, less money, less time, and less material build.