Aha! This is a question that I have been asked a hundred times. I need to ask you two important questions before I dole out advice:
1. What is the spending limit?
2. What is the intended use for the lens?
It is only based on these two answers that anyone would be able to tell you what is "best" for you.
In the meanwhile, I thought that maybe you can have a look at
It outlines some general guidelines while making a camera purchase. These guidelines also help in narrowing on what you want your lens to do.