Upload & Sell: On
Sharp is for knives, axes, and some women's tongues In an image, universal sharpness (whatever that is) would be horrible. Mr. Gardner - as he always does - has provided a superb technical explanation of why this is so. For Photozone or anyone to suggest that Canon's best primes aren't all that good because they are better on a crop camera than a full frame one is just stupidity. Every lens (at least those affordable to mere mortals) has some degree of distortion or softness in one or more of its aspects. Again as Mr. Gardner has noted this is because we are attempting to capture a 3 (really more) dimensional world on a 2-D plane. Fundamental geometry says something has to give.
A full frame camera uses all of the glass and therefore makes one potentially more aware of what is happening at the edges. A crop camera can only utilize the center of the lens which in all cases is a lens' best spot.
Technically the best photos are taken with the largest sensors and the best quality lenses. This however requires skill that can only be learned by hundreds/thousands of attempts. We don't know what your goals are, your experience, or what uses you might make of photos you take thus it is hard to give you any concrete answers.
One generic answer is that in the world of camera gear - with very few exceptions - the more you pay the better you get. There is, of course, infinite arguments as to what the cost benefit ratios are. In the end there are no perfect cameras, no perfect lenses, and no perfect pictures. Any camera, all cameras are compromises. Just pick one up and start shooting.