You gave good reasons for the 17-55, other reasons favor other lenses (zoom range, size, weight, last not least price), so it's often a matter of preference esp. if the af and iq are decent on all possible choices.
Excellent point. In this case the OP is specifically asking for f/2.8, so 17-55 is the most obvious recommendation, but I have used and do recommend the 15-85 as well (http://www.canonrumors.com/forum/index.php?topic=11355.msg202863#msg202863
) in other situations. Like you said, the price and build quality are points in favor, while the IQ is comparable at smaller apertures.
I agree fast prime or FF is the way to go for low light, and I intend to go that route (in that order) over the next few months.