Best clear ive ever used is Motostorms Glamour Clear. (motostorm.com)
SPI used to be my favorite clear, but one day I ran out in the middle of a job, and had to use the Moto I had just got in. Not only did it have quicker build, but it went farther. I was able to mix up the same, or less, and achieve more coverage.
The gloss is the best ive ever seen straight outta the can. And buffs like a dream anytime, being a poly.