[Docrwm]

I got my 18-135 new from B&H. From that source, it's currently going for $460US, and the 50-135 is $899US, so I presume yours was secondhand, Anvh. I don't think there's any argument about the qualities of the 50-135, but there's also not much point in comparing the two, unless you're confining the discussion to the performance in the range between 50 and 135mm. What the 18-135 lacks in optical performance in that limited range of focal lengths must be weighed against the convenience of its having the additional width at the lower end. The result will be different for each person.

Edit: I should say that I bought the 18-135 for the upper end reach, as I was photographing dance competitions and my 16-50 didn't adequately cover the opposite end of the floor. Since then, I've found that the light weight of the lens has provided a benefit to my travel photography.

I would also emphasize that it costs roughly $1000 (yes, one thousand dollars) less than the 50-135 does and does not suffer from SDM failure problems.