So I've found a Sigma 17-50 (with OS) for a pretty good price. I've been considering replacing my kit lens for quite a long time and recently bought a DA15 Limited. It's an amazing lens but I find myself wanting to zoom in some. I was shooting some landscape yesterday with my DA15 and M50/1.7, and found the gap to be quite huge. And since I don't have the money to buy 2 or 3 primes for that range, I've decided to look for a good zoom lens (for the nth time). A few months ago (before deciding on the DA15) I was debating between the 16-45 and 17-70 (both Pentax) and couldn't choose because the 17-70 seemed of higher quality and had SDM, but SDM is notorious for failing... Now I've got the Sigma 17-50 in my sights, which was rated higher here than the Pentax DA* 16-50.
The 16-45 and 17-70 are both cheaper, and I would have to get the Sigma used (or wait a while and save up more $$ for a new one). I've heard some things about the stabilized version being worse than the non-stabilized one. Is that true? Also, does it have common back/front focusing issues like a lot of non-Pentax k-mounts?
Between the 16-45, I would probably choose the 17-70 if it wasn't for the common SDM issues. I like the extra range.
As for use: I won't be using it at the extreme wide end. I have my DA15 for that.
I would use the 20-70mm range (or 20-50), mostly in the 25-40 range.
I also keep coming back to the possiblity of a 28/35mm prime but I am willing to compromise the sharpness of a prime for range and usability -- at least for now.
EDIT: One last thing -- flare resistance. I know I won't be able to get the 15mm's amazing flare resistance from any of these lenses, but I am wondering which one is best in that field.