Sharpness is mainly about the lens and camera. The article "Sharpness: The Deadly Dozen," shows how much sharpness is affected by things like camera movement and your choice of f-stop. (Find it in the February 2014 issue of Outdoor Photographer or online at outdoorphotographer.com.) The best, most expensive lens in the world isn't necessarily going to get you sharper pictures unless you're also paying attention to your craft as a photographer. Cameras and lenses today are extremely good, and if your photos aren't sharp, it's rarely because of the lenses. It's most often because of camera movement during exposure.
Buy your lenses based on the focal length's unique qualities and on what you can afford. Then hone your craft to get the most out of whatever gear you own, and you'll be surprised at how sharp your images can be.