Generally it is best not to choose a free hosting package with more features than you need, and also check to see if the company somehow receives revenue from the free hosting itself to keep it in business.
As already mentioned, it is best to try to get accepted to a more selective free host if possible. Look at other sites hosted there to see what kind of ads are on your site, and the server speed (keep in mind newer hosts will be faster at first). Read the Terms of Service (TOS) and host features to make sure it has enough bandwidth for your site, large webspace and file size limit, and any scripting options you might need. Read free webspace reviews and ratings by other users on free hosting directories. If you don't have your own domain name, you might want to use a free URL forwarding service so you can change your site's host if needed.