I have three options at f/2.8 (a realistic speed, even if it isn't as fast as you'd really like):
Pentax K24/2.8, Zeiss ZK 25/2.8, Tamron 17-50/2.8 A16P.
In terms of resolution charts, the Tamron has the best sharpness over the whole APS-C field,
and has virtually no geometric distortion at 24mm.
But it's not a discreet street lens by any means, especially with the hood,
and it doesn't have the rendering of a prime.
The K24/2.8 has good, but not excellent sharpness, as pinholecam noted.
However, it is cheap, light, and discreet. You can see my review at
https://www.pentaxforums.com/lensreviews/SMC-Pentax-K-24mm-F2.8-Lens.html
(that's the K24/2.8 review page on the forum here, if the link doesn't work right).
The Zeiss ZK 25/2.8 is of intermediate size.
(It does pass my personal criterion for smallness,
fitting in a bridge camera waist-pack when mounted on a K-x.)
Central sharpness is outstanding.
Border sharpness is excellent stopped down,
good wide open if the field curvature matches your subject,
but only fair if the field curvature is working against you.
The rendering is absolutely magic, and it focuses very close.