One of the more widely used ones in the model railway world is Tester’s Dulcote. As with any coating the durability depends on what it is being sprayed over. If it is being sprayed directly onto a high gloss finish it will likely rub off with frequent handling. Sprayed over a more matt surface though it will be much more resistant. I suspect that Colin’s Halford’s laquer is possibly more resiliant, a lot depends on whether the parts are going to be handled or whether you are simply looking for waterproofing.
One aspect I particularly like about Testors is that it is a very matt finish, so looks very good on figures.
Both these vehicles started out with a very high gloss finish so you can see how much the Dulcote knocks it back: