When it comes to durability, I got recommendations from this site to use testor's dull cote and it works very well so far. But for my current project, I want to hand paint the top coat because there are many areas of the figure that I don't want to cover with the coating. I don't have access to an air brush so that isn't an option either.
I recently got this, although i got the 8oz bottle which is $8.50 Americana® DuraClear™ Ultra Matte Varnish only time will tell how durable it is
I like to use future. It's especially nice because it's self leveling so you don't get visible brush strokes. If I want a less glossy finish, I'll mix it with acrylic flat base.