It all depends on your personal requirements etc.
A
VPS Hosting gives you a dedicated environment (exactly like a
dedicated server - but you wont have as many recourses).
With a
VPS Hosting, you can control all aspects of the server such as apache configuration, PHP configuration, and firewall configuration.
You can create reseller accounts and standard hosting accounts with a
VPS Hosting.
Obviously, if you do not require this functionality, you can simply upgrade your reseller package - but this won't give you the flexibility of apache configuration etc.