I've been using Vallejo Brush on, mat and gloss, diluted with destilled water, and shot through an airbrush.
2 coats of gloss, one or two coats of mat depending on how effective the first coat is.
It's gives a good level of protection to the figs, and has given me fairly consistant results.
I have had a few problems with clouding when shooting the mat, especially with blacks and dark greys.You just need to be careful to put on a really light coat and let it dry for at least 8 hrs, (says 4 on the bottle but better safe than sorry,) before repeating.
What Orctrader said is excellent advise, if you know you're going to varnish the fig, and that varnishing dulls down the colours and flattens contrast, then paint accordingly. Exagerate the contrasts and don't worry so much about super smooth blends. It can actually speed you paiting up.