Depends on your shooting preference. Do you shoot in low light often? What is your most used focal length?
By the way, maybe you want to have a look at Sigma's 17-50. I find Tamron's build quality poor. Used for 2-3 years and the rubber for the zoom mechanism came off.

I dont think we only need expensive lenses for use with our dslr. as we can see from the list, the most worthy lenses are those like 16-45 and the 50 1.8. i have tested 50 1.8 before and im definitely impressed.if it is priced more or less like canikon, im definitely getting it.

btw, some news about pentax lenses

http://photorumors.com/2013/08/27/pentax-t...ular-apertures/

instead of coming up with new lenses, they come up with new coatings. but theres still hope for new lenses though.

i think its very expensive and i dont need or even use flash that requires weather sealed quite often.so i might just give it a pass.