Image quality is partially subjective. From what I recall seeing around here, both lenses are very good. The objective differences between the lenses include:
Pentax DA 200 advantages: Weather resistance, smaller size, less weight.
Sigma 70-200 advantages: Zoom versatility. 200mm is too long for many indoor events.
P.S. You didn't say whether you plan to buy new or used. I think the Sigma 70-200 is discontinued in k-mount. The Tamron 70-200 is another option and still available new.
---------- Post added 01-25-15 at 09:50 PM ----------
Originally posted by morgun My main interest is wildlife, so wr is a consideration but not the only one. I was hoping someone who has used both could tell me which has better af for example, what do they perform like with a tc
For wildlife consider the DA*
300 instead. A 200 paired with a 1.4 TC comes out to 300mm/f4, but is more expensive (unless you already have a good TC) and probably won't match the DA*300 image quality. Plus, you can later add a 1.4 TC to the DA*300 if you want even more reach for birds and other small animals.