If at all possible, grade your plan levels in a descriptive way, usually describing their use or who will use them.
Here's an example from Cannybill.com:
Instead of the "
Crap" "Okay" "AWESOME" style of goading people into buying the most expensive plan you can use these descriptive names to show who is using the plan or why, for instance you could have "Personal", "Professional", "Small Business" and "Enterprise."
Personal is cheap/free and is missing features, but most users won't need them. Professional is a full featured suite for people that need advanced features. Small Business and Enterprise may have various amounts of support or infrastructure dedicated to that plan that might be irrelevant for a single user.
Cater this idea to the specific user groups and pricing plans your product has and you should help eliminate confusion (I'm a professional user, do I need the Premium or Regular plan?) and sidestep the image of one plan being "better" than the other. They're not "better," they're different!