SUPREME

Looks like you are Prime already,congrats.

Now,as to whether Supreme is worth,you be the judge of it.
Personally,I think Prime is the one necessary by all means. Supreme simply gives you more cosmetic options,more FREE unlocks and the ability to have your name changed.
Also,as with each upgrade,you can give more reputation,considering you are a more invested member.

Btw,once you have an upgrade,it's forever,so you can't un-have it.