they appear to be pretty much the same (wouldn't surprise me if their panel is actual the same). The DELL is possibly better at its color reproduction since it claims 85% accuracy and the Acer doesn't claim anything at all. But since this isn't a 'U' series DELL I can't vouch for how much water that holds.
Personally I like the DELL they have surprising quality in their monitors especially if you go higher up and get one of their good stands which are frankly the best only beaten by a full blown monitor arm.