Most of the time when it comes to selecting the best lens we just look at the Brand and Price. There are many sites that let the general user compare different lenses, but you need to have a very good understanding of lens technology to interpret them.
There is a site that will let you see what you will get from for the money and anybody understand it. Here you can compare a Canon, Nikon, Sigma or Tamron lenes.
This link is to a lens comparison tool that gives you “ISO 12233 Chart 100% Crops”
How to use the tool:
What you do is select the lenses that you wish to compare. You have a choice of f-stops and if it’s a zoom lens focal lengths. All you do is move the cursor across the images to compare the image quality.
This link is to the best lenses that Canon and Nikon make (200mm f2 prime) and the price > $5,000US. This is so you can see what all lenses should be like.
This link is to the ISO 12233 Charts help page for those who want an in-depth understanding of the tool.
Let me know if you find this helpfull