Best plugins/approach to use for upgrades/levels

I’m building out a new site on WordPress MU and am trying to find the best plugins to use to accomplish what I need.

With the different options out there like pay-to-blog, supporter, upgrades, etc. I thought I would ask here to see what would be best by the people who created them and those using them.

I’d like to offer 3-4 levels of blogs on my site.

The first level will be free and will show ads on it.

I would also like to restrict some functionality of the blogs.

The second level will do away with advertising and be a basic WordPress MU blog with a couple plugin additions.

The third level will add a few more useful plugins as upgrades.

The fourth level isn’t determined yet but I didn’t want to limit myself yet.