If you are going to buy just one size ball, buy this one!
These balls are great.  I watched a friends video, Treat while you Train Self Help Kit, so I knew the basic concepts.  The problem was I didn't want to buy an entire package.  So after reading many reviews, I settled on my first pair of balls being the Alpha Twins.  So glad I did.  Even in my neck area I found these to be a great size!  Wonderful for reducing muscle tension and winding down.  Even has eased up several headaches.
Rating: 5 stars