Tamron 28-75 is the ultimate portrait lens on APS-C length and speedwise imho. For walkaround I always wishes that it's 24mm on the wide side, but these days I often bring the Sigma 10-20 or the Takumar 24 for its companion anyway, so wides are not a problem anymore....
Both are really great lenses, build quality is very similar I think, but the 28-75 is usable on film cameras, a little bonus (not that I ever use it with my film bodies... it's just way too heavy for them). In the end you should go with the length that fits you best, choose: 17mm or 70mm?
Zoom ring wise I find the tamron very close in quality and ease of use with the kit lens.