Well yamaguzzi, I guess that you will now know that there as many opinions on tyres as there are brands and models out there!
Just to add my tuppence ha'penny worth of opinion...since having K100's, I have always opted for putting Avon Roadriders on them and they've done a good job come sun, rain or occasionally something a little slipperier. Probably not the sportiest tyre out there, but suit my riding style of occasional touring and a 70 mile round trip commute every work day.
When I rebuilt Gretel following my off last year, I decided that I'd try a different brand and put a set of Dunlop Arrowmax Street smart on front and back. Initially they were OK, but for the last few thousand miles the bike has taken to wallowing and wobbling when crossing ridges - an especially uncomfortable feeling if that ridge is the white line in the centre of the road when overtaking! Yes - it does feel that sensitive. I normally run with 36psi front and 40 psi rear (one up, unloaded). Knowing that low pressure in the front is not good, I have tried upping the pressure to 38 psi to see if that made the handling any more stable...it didn't.
Anyway, having watched the clip that Ed posted and hearing that one of the brands was prone to twitchy steering because of the pointy tyre profile, I wondered if I was actually making the sensitivity worse by increasing the pressure so decided to reduce it to 33 psi (the pressure quoted for a K100 front tyre in the Haynes manual) and see if that makes a difference - I'll let you know when I get home tomorrow (I carry a battery driven air pump...so if it is horrible, I. can pull over and squeeze some more psi back in). While I was at it, a quick check of the rear revealed that some more urgent attention was required as the rear was down to the canvas in places. If I needed any reason to revert back to Roadriders, this was it. When I had my annual state inspection (MoT) at the end of August, I got an advisory on the rear tyre as it was approaching the wear limits, but I reckoned it had about another 1000 mile left in it. As of today, it was clear that I had successfully used up that 1000 miles (I had actually done just shy of 1100 miles)! As you can see from the following photos, the centre section has worn very flat and that certainly will have contributed to the wallowing experience - perhaps I need to corner faster to use up more side wall?
Now, looking back at my records...I have previously got just over 9,500 miles out of a Roadrider rear tyre. The Dunlop Arrowmax Streetsmart gave me a miserable 5389 miles. I won't be using that brand on a K100 again.
So long story short, yeah, Avon Roadriders gets my vote as a good all round tyre.
Update 10 Oct 17: ....and the verdict is....oh the joy of rolling around corners again and overtaking without a worrisome wobble as I cross the lane markings. Mostly down to the back tyre I think (you can see how flat the not-so-old Dunlop had become) but I certainly had no issues with the slightly lower pressure in the front tyre and the steering certainly seemed less twitchy. Despite heavier than usual traffic, I made it to work 5 minutes quicker than recent previous journeys too!