Looking for a vacation super-zoom. I have the Fiji 18-135, but I am wondering if the newer Tamron 18-300 would show better image quality in the 18-135 range?
Don't know about image quality, as never compared them. Can only say that once I got the Tamron 18-300 it pretty much replaced my 18-135 because of the much needed (for me) reach. YMMV.
On the wider end, the Fuji is better than the Tamron in the center and corners. Maybe 100-135 the Fuji corners tend to drop off a LITTLE, and maybe then it is closer to the Tamron.
But these are not going to show much difference in sharpness in reality. One shouldn't try and compare that with these 2. if you need ONE lens, AND longer than 135mm, then you probably need the Tamron (which isn't stellar across the entire range).
The better option, if you want sharp and clear, keep the Fuji 18-135, and add the Fuji 70-300... But I think you want one lens.