Both are very helpful, if you can get your insurance company to allow you to have one or the other it will be very good for you. You should also be given a prescription muscle relaxer to assist the tens or ems in the job it is trying to do. There are many different muscle relaxers our there, I have used the majority and now I am back with the old flexeril because it seems to be decent.
If the doc prescribes something like soma (carisopridol) it is an excellent medicine but do not under any circumstance try to drive or work until you get used to the affects of the medicine, I am a drummer and the first time I took soma, the band was just staing at me tring to figure out what was wrong with me. It is a great med but man it will really scare you because it makes you feel totally out of control for about 30 mins.
Good luck,
-brian