Hi luicam,
Thanks for posting a question. I'm more than happy to assist you. Here's a link to our webpage that compares the shared hosting packages:
Comparing Shared Hosting Packages
The Pro Plan gives you about 4 times the resources such as add-on domains and MySQL databases. If you're looking to expand and host more websites (more than 6 separate websites) than the Pro plan would be better.
Keep in mind you can upgrade hosting at any time through AMP. Here's an article explaining how to do so:
Upgrading your Hosting Plan
If you need further assistance please feel free to contact us.
Thanks!
Tim S