I have both. The difference is actually pretty straightforward. The Basic Reseller is selling hosting, domains, and other actual web-related services. The Pro Reseller is getting others to become a Basic Reseller. Its similar to a 2nd level on an affiliate system. There is no multi-level tiered part of it as I understand.
With both plans you get resources to promote your business. For example, you get a managed wp account to setup advertising and demo sites to showcase your skills. These resources are not on the developer level, but are sufficient to put together some good demos. You also get some email services, a basic SSL, and a few other goodies.
The commissions off of the Basic Reseller are more generous than the Pro Reseller. This makes good sense in that margins can only be divided so far in order for GoDaddy to maintain reasonable suggested retail prices. You can set your prices higher than the suggested retail, but I don't think that's a particularly good idea in most cases.