Well, Medifast & Nutrisystem are two very different programs so it really is a personal preference thing. I looked into Nutrisystem first & didn't like that it was mostly tv dinner type food...the higher carbs & sodium scared me. I'm sure some of the NS folks will be by to add their thoughts.
I lost most of my weight using Medifast. It is easy & yet not so easy. By that I mean that it is easy to have the various 5 Medifast meal replacements (shakes, soups, oatmeals, puddings, bars, etc.) + 1 healthy meal of lean protein & veggies a day. Not so easy in that you HAVE to stick with the plan & follow their directions to realize the rapid weight loss.
Both are good, but different plans. With Medifast & I think Nutrisystem, you can order a 2-week supply & try it out for two weeks to see what you think. Hopefully others will chime in with their thoughts. Good luck on whatever diet you chose to follow!