Which is best tens machine for shoulder pain?

Lots of options: There are a lot of different tens machines on the market and each manufacturer will tell you why their machine is better than all the rest. I have been unimpressed with the differences. I would check with your doctor or, if you are paying cash for one, look on ebay and try one of the less expensive ones. It may work just fine.

Which helps: Tens units are very personal and depend on the level of stimulation and the placement. A good physiatrist should fit you.