I have, I think, two all-time-favourite AF lenses in K-mount on the APS-C format... The first is the Tamron 28-75mm f/2.8, which some might think a rather pedestrian and limiting choice - but it's a reasonably fast constant aperture lens that covers my most common focal length preferences, is sharp enough for me (since carrying out AF fine adjustment), and renders to my tastes. The second is the flawed but - for
me - quite wonderful Sigma 30mm f/1.4 Art, offering a near-perfect field of view for general photography and rendering to die for, like a modern interpretation of a classic film-era lens.
But...
My favourite lens
for this year is one that I've only quite recently come to use regularly and value so highly... my screw-drive HD DA55-300 f/4-5.8 WR.
For some time, I've been (and remain) a huge fan of the DA*60-250 f/4 AW... It's beautifully built and optically superb - but it's not without its quirks; specifically, toe-curling focus breathing at short range, leisurely AF, plus the bulk and weight that come with a fairly fast, constant aperture AW zoom with excellent optical performance. Because of these quirks, over the last 12 - 18 months I've increasingly chosen to carry and shoot the HD DA55-300 instead. It's limited by the variable aperture, of course, and the build quality - whilst very good in its class - isn't comparable to DA* lenses... but I've been very impressed with it optically. Yes, the DA*60-250 is better - but it's not a "night and day" / "chalk and cheese" difference. The little screw-drive 55-300 is amazingly capable, and the compact / light-weight build means I'm more likely to carry and shoot with it. In fact, I
have carried and used it considerably more than I would the DA*60-250 in the past year, and I've ended up with a significant number of "keepers" for my photographic library as a result.
The OP suggested including a couple of photos to support the choice of lens, so here are two taken earlier this year at a bird-of-prey conservation centre at Kielder in Northumberland, not too many miles from my home in the North East of England. These were shot in relatively poor daylight on a grey, drizzly day - and, hence, at higher ISO settings - forming part of a larger set that I was delighted to capture...