<p>The type of lens (prime/zoom) effects how likely a lens may need service and its out of box, new performance. Performance variability and reliability are significantly better for prime lenses. (Roger Cicala's lensrentals.com site is probably the only place on the net to get non-anecdotal, statistically significant data on lenses, since they have 100's of the same lenses and test them when they return from rentals.)</p>
<p><em>Out of Box</em> performance is critical regardless of what type of lens you buy. It's easy enough to try the lens out and see if it performs well in the store before buying it, or to bring it back in a couple of days, if needed, before leaving the country. Make sure you can bring the lens back for an exchange or refund.</p>