Probably the supernova. Because two tennis balls taped together works almost as well as the Gemini. Haven’t found anything yet that compares to the supernova. Great for hitting hamstrings glutes and heinous on the TFL.

Michael–
I would recommend getting the both. You won’t be disappointed by either one.
Both kick it up a level and show you more.
Some would depend on what areas you are doing the most work with. The supernova is more versatile, but
I haven’t found anything that is as good as the Gemini for T spine. Way better than 2 lacrosse balls taped together.
On both of them you don’t know what your missing until you are exposed to something that is better than what you have. Both of these are an upgrade on options that came before it.

Definitely go with the SuperNova if you are choosing one over the other. Two lacrosse balls taped together are good enough for most things. (However, due to the tape you won’t get the same tackiness as you would otherwise.)

I’m planning on getting both whenever I have the cash. They are just upgrades and look less ghetto/sketchy when I travel through airport security. I’ve been stopped sooooo many times for having two balls taped together, some bands, softball, and a pipe/roller.

Also, I feel it helps support MWod and I’m all about that.