Naming the premium version of your product

Hi all

I have a niche SAAS product that currently has over 16,000 users. It's currently free, but I'm about to launch a paid version (there's a reasonable learning curve to using the product, so I have decided to keep a basic free version).

I wondered if anyone had any experience to share in terms of naming a paid version of a freemium product.

Off the top of my head, I've seen the following used:

• "Pro" (I don't like this because it implies that in order to subscribe you need to have a certain type of expertise)
• "Premium"
• "Plus"
• No particular name - just "Become a subscriber" or "Become a supporter"

I'm tending towards "Become a subscriber". It's boring but accurate. Any input appreciated; thanks!