I use the DA 50-200 because I have it.
I bought it 9 years ago for my IST-DS, and it has served me faithfully. I like its convenient small size and its AF is faster on my K30 than on my old IST-DS.
I also have the all plastic FA 100-300 f4.7-5.8 which I use when I (seldom) need a very long range on the K30.
I know there are better telezooms than these 2, but I dont shoot a lot above 200mm. And when I do plan long telephoto shoots, I can also use my Fuji X-S1.
When I want to travel light, I am happy with the DA135 as my only lens on the K30, and a small compact as a spare and for hiking, social events or candid photography (either my X10, which is a joy to use, or the very pocketable XZ10 which looks like a casual point and shoot but has many advanced features, such as a ND filter and a very fast lens).
I consider I already have quite a lot of lenses, which suit my needs, so I am not interested in buying another zoom, even if the F 70-210 seems a good and compact AF lens.
I may buy new lenses in the future, but it will rather be the DA70 ltd and DA21 ltd or DA 20-40 ltd.