Once you've added at least two fonts to your collection you can compare them closely by overlapping them in the compare view. Simply click the review tab at the bottom and navigate to compare tab at the top.
This repository was designed specifically for web designers. As such it shows the impact of the font choice on page load time, allows selecting only the font styles and sets you need to reduce overhead, and gives multiple methods of integrating the fonts into your website.
Within categories such as serif, sans serif, monospace, etc, you can adjust desired thickness, slant, width and script to filter the collection of fonts. Additionally, you can also set how you wish to order the fonts (by popularity, alphabet, date added, etc).