The best zoom lens on the market is your feet.
No zoom lens on a SLR can come close to a prime lens and no prime lens on a SLR can close to one on a rangefinder, fixed lens camera, or plate camera. It is simple optics.
If you feel that you need to use a zoom there are two pressing related questions:
Why do I need a zoom lens?
If the answer is that you need a zoom lens because what you like to photograph is often unapproachable on foot and you have little control over where you can stand to make your photographs (perhaps because of a physical barrier or terrain that prevents you or some gorilla like bodyguard/security guard, etc) then the need for a zoom becomes clear. In this instance, all considerations of barrel distortion, widest aperture, quality of the optics, etc become irrelevant because it is your only way of getting an image.
My question would be do you really need to make a sub-standard (in technical terms) image? - if yes then use a zoom and accept it has limitations. If not, go back to my first sentence.
Bests,
David.
www.dsallen.de