Go with the 18-135 WR. It is really a nice lens and as others have said before, there isn't that much difference. Check out my smugmug account link here. All of the shots with the whales and the iquana's in Ecuador and the shots from Qatar are with that lens. For primes you might want to consider some of the older K-Mount pentax lenses. The Halloween shots are with the Pentax A-50mm 1:2 and all of the group shots on the Heritage Oaks are with an Albinar M 28mm lens. The others in the Heritage Oaks are with the Pentax DA 50mm f1.8 lens that you are considering.
http://kcs-photography.smugmug.com/
Last edited by kchamber4; 12-02-2014 at 09:51 AM.
Reason: Forgot the link