I like Golden Polymer Varnish with UVLS
for large works and Krylon Gallery Archival
for small. My gold standard is super duper uncomplicated: Does what it says on the tin.
Both products do. I've only used the Golden Satin varnish, but it is a nice true Satin, goes on evenly, and gives a coating that feels sturdy. Ditto for the Krylon - I've used all 3 finishes, and again.. the Gloss is is a nice hot shine. Satin is pleasantly satiny. Matte is matte. What more do you want?
I will say this: USE AN ISOLATION COAT!!!
I followed exactly Golden's steps for applying their varnish (see link above), which includes putting a clear isolation coat over the entire work before varnishing, and I'm beyond glad I did: I would have been dead in the water otherwise, following a client-requested color change that required me to strip the varnish off and re-work a section of the painting. There were small areas on the sides of the canvas where I'd obviously had a lazy moment and not gotten a good coat of the isolation clear on, and the ammonia stripped the paint right down to the gesso. Lesson learned the hard but grateful way! The VERY LARGE (about 36" x 48") section that I needed to adjust the color on had a good isolation coat, and came through the varnish removal just fine. Since the isolation coat is nothing but a solid layer of clear acrylic medium, it's completely safe to paint over.
I haven't yet had to remove the Krylon varnish, but I still apply a clear isolation coat to all of my works prior to varnishing. The experience of stripping the Golden varnish taught me that a good isolation coat can withstand pure ammonia being applied to it without damage to the underlying paint layers - and I paint extremely thin, with a fluid acrylic technique.