Originally Posted by
GrumpyDiver
Debbie - one significant error in your assumptions, the "different range" as you put it is related to the sensor, not the lens, so in the 28-300mm range both lenses will perform identically when it comes to what you see in the viewfinder and what you record in the camera on your D7100. The DX lens will get you an additional 10mm focal length at the wide end, and this is really the main difference you will see in practical terms.
From a build quality, both are going to be similar as they are really built for the same market. Both have optical quirks, due to the wide zoom range that they cover; the 28-300mm has some strange distortions and the 18-300mm exhibits some softness at the long end. You might get a slightly better image on the 28-300mm lens as you will be shooting with a lens with a wider image circle, but I suspect you would have to be pixel peeping to notice the difference. If shooting jpeg, the camera will compensate for the distortion, and depending on the raw converter you use, the same will happen if you select the appropriate options during the raw conversion process.
If you were looking to go FF in the short term, I would definitely suggest the 28-300mm FX, but as you are looking at that as a low priority, I would go for the DX lens to get the extra range at the wide angle side.