I tried some art store acrylic inks a while back and didn't like them at all.  Cant recall the brand.  They just didn't "behave" in terms of getting into recesses and panel lines and such.  Other brands may well be completely different though.

I think I was one of the first to ask Elm for GameColor Inks (before they came out with the ModelColor Washes) and have been using them ever since for my washes and panel lining.  I like to cut them with a bit of Glaze Medium so that the effect is not so strong, flows better (less chance of tide marks), and longer cure time (ie time to fix mistakes).