Have to admit that I prefer the GW washes to Vallejo. I so wanted it to be the reverse. Vallejo is cheaper, matches all my paints and doesn't come from the evil Empire. However the Vallejo seem to be 'grittier'. I am experimenting by adding a little matt varnish to try to smooth them out. The range of colours for Vallejo is excellent, the umber is great and they have just released a blue and green which are much darker than GW and look really useful.
I have been painting a batch of WW2 Russians by blocking in the colours using the highlight tone and then a wash. The results aren't going to win me any prizes but my ouput has rocketed. If you are into gaming and need to clear the mountain, this is a good way to go.
John