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.
EOS 5DIII, EOS 6D | Rokinon 14mm f/2.8, TS-E 17mm f/4L, EF 24-70mm f/2.8L II USM, EF 35mm f/1.4L USM, EF 85mm f/1.2L USM, EF 100mm f/2.8 Macro USM, EF 135mm f/2L USM, EF 70-200 f/2.8L IS II USM, 1.4x III, 2x III | 600-EX-RT x3 | EOS M + EF-M 22mm f/2