Which should I choose? Pro Sites or Membership?

This will be for a WPMS/BuddyPress install.

I need to allow people to sign up for free and be members for free.

I need to be able to charge them a set fee per blog up to 4 blogs. After they are paying for 4 blogs any after that are free. I need to allow them to return lower than 4 blogs without issue.

I also entertained the idea of one free blog, then have the above scenario (1 free, 1,2,3,4+ paid.).

Which plugin should I look at getting?

Also, the Stripe gateway looks very nice, it's not available for Membership is it?
Will it be in the future?