I've used all kinds of varnish and love Epifanes and it's the only kind I use.
Are you using the Wood Finish build up formula or the Clear Gloss finish coat. I never thin the Wood Finish by more than 20% on the first coat and not at all after that, putting on about 4 or 5 coats, all within 24 hours of each other, then sand. I use Epifanes own thinner. Next I put on 2 or 3 coats of the Clear Gloss sanding between each coat. I never thin the final coats.
I also have found that using a Black China bristle brush works best for me(and don't make it to thick a brush). They hold just the right amount of vanish and will not let you put too much on. Problems always come from too much varnish, not too little.
Hope that helps,
Paul