Upgrading from Pentax 16-45 f4 - what to buy?

Its not that the lens is no good - I just have a bit of money set aside for a new lens and thought id upgrade the one i use most to a more versatile option

I have the 16-45 which I used for travel. Despite it being a fantastic lens and sharp across the frame I found that in tropical places with really bright sunshine that lens flare and ghosting were unacceptable. I always used the lens hood. Then I got the 18-135 and really like it but missed the 16mm end, so I now use the 16-85mm which is easily the best lens I've ever had IQ wise. My first two copies were dud, 1st dead on arrival and 2nd defocussed.

I prefer the rendering of the 16-85 to that of the 16- 45.
I used the 16-85 for this lot here soon after I got it. Very pleased with it.
I don't like the way the 16-45 increases in length when it zooms out as it gets in the way of the onboard flash. But lack of sharpness isn't one of its problem.
It would be worth swapping a 16-45 for a 16-85 mainly for the increased versatility. I've not experienced the focus/decentering issues some have reported. I'd be curious if anyone spots an issue in those Micklegate photos I just linked to.
As to a 16-85 vs an 18-135, one can crop an 85mm picture to match the framing of a 135 photo, but the reverse isn't true (one can't turn an 18mm exposure into a 16mm one.) That is if one prefers a single lens solution and architecture is a common subject matter as opposed to sporting events where the extra reach may come in handy.
I've not considered a 16-50 given the repetitive reports of SDM issues.

If this had crossed my mind 8 months ago, I would have now been the happy owner a of 16-85 instead of the 18-135. It makes perfect sense.

(only so far though so it does still depend on favourite subjects.)

The first thing I did when I got my DA16-45 was to dump that useless hood. I've never seen any great flare or ghosting problems with it.

I bought a Sigma 17-50 f/2.8 EX DC recently because I wanted a mid-range zoom that was better than the 'kit' 18-55. It had been given some good reviews. I found it to be very sharp in the middle, but disappointingly fuzzy at the edges, esp at the wider angles. In fact, it is then worse than the 18-55! Maybe I have a poor specimen?
It does have the advantage of a constant f/2.8 and when I tried a few photos deliberately into the sun, without a lens hood, I can see no sign of flare. Good in that respect.