Varnish usually ends up being a spray version that you like the finish of. Best thing to do is create some test pieces with the paints you use and try out the different varnishes you have in hand. It’s hard to get that far in a piece, only to lose what you wanted to a crappy drying clear, weather induced cloudiness, or even excessive orange peeling. Durability wise, automotive type clears(sprayed with an airbrush or paint sprayer) are probably the best and have different finishes(but costly). Rattle cans work well too, but I still go back to paint compatibility tests and final look once completely cured. Testing can fun too, imo.