Ok a bit of a naff question and I can already imagine some of the responses I'm going to get but...
I'm in need of a lens that goes a little longer than my 20-40, which has rapidly become my favourite (Well this week anyway)!
Not fussed about macro but I suppose it may bite me one day and then I'd have one, needing to lighten the kit a little and some upcoming shoots require a lens with a narrowish DOF, also a fisheye but thats another matter...
So, I'm going to have to get shut of my beloved 12-24mm because these upcoming shoots will pay me money, I need the longer lens before I need the fish and I do not have any readies left at the moment for any more lens addiction, without losing one first... And she who must be obeyed has spoken!
I will eventually have to buy both the 10-17 and the 70 or 100 but not both of the latter, as I just can't take the weight of too much kit up onto the high peaks anymore, I don't like passengers and I'm re-building my kit to just what I need and willl use.
With all the extra clothing, grub, poles, tripod and other parafinalia the Rucksac is starting to weigh heavy and no longer such a joy to carry.
So if any own and use both for non macro purposes, which makes it into the bag the most, So then, which and why?
Sorry for such a daft question on two totally differing lenses, Oh and please do not offer any third party contenders, as, since none of them support R/Pentax much anymore, I refuse to support them at all!

Ok Paul I'll be serious for a minute (It does happen occasionally)!
Nowt wrong with the IIs at all, the K3 also does a lot of things right, and IMHO, better, having the whole focus array able to see in -3 EV is brilliant, I find with the K3 my "Hit rate" on moving objects, is about the same as it used to be with my old D300/s, as in pretty good but like those bodies, it requires a little learning, all comes with practice, I don't forsee the K3-II being a whole lot better but we'll see, I'm currently out on purchasing one and it'll take some pursuading to change my mind too!
Most that use Canon and Nikon, seem to be happier with their respective Camera's than those from here that try to shoot fast moving sports and action but if you know your subject matter, then you'll do fine. That is more important than a camera you just need to wave in the path of a passing jet to get a sharp snap.
Practice at the local Airport get your eye in a bit before you go to an actual show and you'll get a better success rate than many with just a zoom Bridge camera, let alone a DSLR!
Lenses: Now I have no doubt the new Pentax 150-450 will be the dogs danglies, expensive but in context not really any worse than the CaNikon duopoly, it would seem from what I have been told, that were only going to notice any quantifiable difference in focus ability on these new lenses (70-200 and 150-450) rather than the old SDM ones. Not sure how that works yet but I'll find out, it leads me to believe the last firmware update for the K-S1/K-S2/K3, which had "Optomisation" for the new lenses incoporated as well as the required upgrade to work the focus hold/memory buttons etc, may well have included newer algorithms to operate the new lenses more efficiently (Supposition). Now there is not a lot wrong with the SIGMA 50-500mm, I have found it to be quantifiably superior to the 150-500 but the latter is not rubbish either, get the HSM ones, not the screw drive, I have found that the screw driven ones while they may actually be faster focusing are not as sensitive to changes in subject direction and motion. They are now available new and second hand for reasonable prices and there are a few of them about, I think there may be one in the classsifieds actually!

"Where as Nikon and Canon are just common"
Yep! Common!

Jump!
Regarding Sigma and Tamron et al, they are not going to support Pentax K mount any time soon, and you can either stump up £2000 for a boat anchor, or buy the DA*300 with the HD convertor, or...
Jump!
Branded something to 400's are no cheaper than the Pentax but you can get a something to 600, lens from Tamron and Sigma for half the price, so for the third time...
Jump!

Addendum: People who need autofocus to take pictures will tell you that Canon and Nikon have better focusing for Airshows and Birds in flight etc, so perhaps you'd be better off with one of those systems? (Psst Don't tell John Riley I told you that!)

Beware, auto translate!

https://translate.google.com.au/translate?hl=en&ie=UTF8&prev=_t&sl=ja&tl=en&u=ht...

"PENTAX if diffraction correction chrysanthemum"

Don't forget that most of the front end of the 12-24 is metal, it's a fantastic lens, my go to for most of my wide Landscape stuff, wipes it's bottom with the 16-50mm F2.8 in the overlap, sample variation may be at play here but I've had two 12-24's both have been good and three 16-50's, all have been bad, or not as good as they should be, two optically and one mechanically, it is a street ahead of the 16-45mm F4 IMHO as far as build quality and especially mechanical quality is concerned, optically, I have no idea as I've never owned it but it gets a really good rap from the American site...

The full frame prism OVF in my old Sony A900 (big and beautiful to behold), cost Sony £178, then on top of that they had to employ an artisan to make sure that each was aligned 100%, something they did not do with the much cheaper but very similar spec A850 (Mores the pity, the viewfinders on those including mine were misaligned by up 10% ! :shock. Point being that next to the FF sensor the biggest cost item in the camera, was the viewfinder. Now I know that the "current" Pentax finders are not FF (Still hate that term!) but they are 100% and made to very fine tolerances, now an APSC sensor costs around £40-£50, (Slightly out of date reckoning here :blush but I bet the finder costs more...

The more I look at the K-S2, the more I think it will be my next camera and not the K3II, for those very reasons mentioned above John...

AND SHIPPED...

AND SHIPPED...