I find myself a bigger fan of Vallejo, thanks to the way the paint covers for me and the fact that Vallejo makes a lot of great colors for historical models (or historically inspired schemes, for that matter). That being said, it's not that I hate Army Painter; I am happy to use them if I can't find the Vallejo color I need, either due to Vallejo being out of stock where I happen to be shopping (a common issue), or Vallejo just doesn't make quite the right shade.
Oh! And I am a big fan of the Army Painter shades!