Is bro, is it true that kit lens with any filter will have more vignetting as compared to other lens like the tokina 12-24 or the 50mm f1.8
That is certainly true.. HOWEVER..
18~135 is more flexible than those other lens u mentioned.. walking around with that while traveling is alot better.
Considering the $$ u pay for your kit lens.. its among the best u can get in the market today.
Having said the above, I must say those lens you mentioned are great value lens.. should buy them all if budget allows. I've got the 18~135mm kit lens and 50mm 1.8. I'm seriously looking at tokina 12-24 and hope to buy one soon.