There are more faster and cheaper lenses available around 50mm than around 28mm. If you don't mind manual focus and stop-down metering, you can get a 50/1.2 Pentax or a 55/1.2 Cosina, somewhere around $250-350. You can trade price, speed and convenience features to get exactly what you want from $25 on up through the Pentax-DA 55mm f1.4 with weather seals and SDM.
At 28-35mm, fast choices (let's say f2 or faster) are limited. The Sigma lineup looks very competitive on paper, and I think they are well-priced. Pentax has a DA35/2.8 lens that's not fast, an FA35/2 lens in short supply/high demand, an FA31/1.8 that's quite pricey, and some long-out-of-production glass in high demand.
Of these focal lengths on APS-C, 35mm feels the most like a normal lens to me. I have a couple of older fast 28mm f2.0 or faster lenses, and they still feel a little wide. I just got this, an older manual-focus model of the Sigma 28/1.8, after looking at the AF version a lot:
It's already a hefty lens. I can see why the #1 issue with the AF version is size. I haven't used it enough to really compare it to other choices, and they are somewhat rare. I think it's odd that the AF version has been out for a while, gets very good reviews and no more detractors than any other lens, has less and less direct Pentax competition every day, yet few people buy one.
If you have the kit lens, it should be a good tool to select focal length. Just try to live with one focal length for a while. That will at least limit your search to one range.