The smaller the zoom range, the better the image quality, all other things being equal.
I must disagree with this; to a HUGE extent, what determines zoom lens quality is NOT the zoom range--it is the initial retail price point AND the generation of the lens. The above quoted statement and its reference to
zoom range being the key quality determinant is outdated thinking, and ignores the simple fact that _modern_ zoom lenses, ones that are designed to be used on high-resolution digital SLR's these days, can be extremely good performers, and the HIGHER the initial retail price, and the more quality emphasis the maker put into the lens, the better the lens will perform--even with a wide zoom range.
A low-end lens like an 18-55 kit zoom, one that retails for $99 as part of a kit is quite often only average at f/4.5 to f/5.6, which is near wide-open, or totally wide-open...yet a $999 to $1,500 zoom with a 5x focal length ratio can easily better a $99 lens. Same thing with _MODERN_ high-dollar lenses like the 28-300 from Nikon: QUITE a good lens...or the 200-500 Nikkor zoom...or the NEW 80-400 AF-S. All these are good lenses; the new 80-300 VASTLY outperformes the old one ( the one I made thousands of great pictures with back in the 4- to 10 megapixel era) because it is 1)much newer than the earlier 80-400 and 2)It was DESIGNED and priced to be a good zoom.
The old-days advice of "high zoom ratio = "crap lens" is not valid, as far as it goes. One must take into consderation
the quality and price point that the maker designed the lens to be built for! As well as the design ERA...old-time lenses with regular glass, no aspherical elements, NO nano-crystal coating, etc,etc,no VR, and low price are often not all that hot on today's digital cameras..
Here is a GEAT example of an on-line review that shows the 28-300mm Nikkor VR zoom is a FINE lens...
Nikon 28-300mm VR Review
Why? Because of everything I mentioned above; NEW-era design...HIGH priced, multiple ED glass elements, multiple aspherical elements...built to be GOOD, for NEW-era digital capture.