I have used both Jenny Craig and Nutrisystem so here is the low down...
Cost: They are both on par. If you want to go cheaper on either there is a way, on Nutrisystem if you order the "flex plan" you do 20 days a month on the plan (weekends on your own food). With Jenny Craig, you don't have to order all the food and you only pay for the food you order. I prefer my Special K to their breakfasts so I don't order breakfasts, I prefer fresh fruit for my snack/dessert so I don't order them either, only the breakfast/lunch/dinner and the nutrition bars (contain your daily vitamins and minerals).
Convenience: Jenny Craig is better as everything is included in the daily menu, you can add more fresh veggies/fruit etc. if you want but it's not necessary. Most JC foods are frozen and need to be microwaved. Nutrisystem has products that need to be prepared (they don't really mention this up front) like scrambled eggs, you need to mix with water and cook, cakes you also have to mix and cook, pancakes - same thing. I find Jenny Craig much easier. With Nutrisystem you must add vegetables, breads and proteins as well as vitamins to get your daily nutrients, so that must be thought out in advance. With Jenny Craig, all food is included and the nutrition bar that must be eaten daily contains your daily allotment of vitamins and minerals.
With JC, you must go into their office weekly for weigh-in, session with councilor and to pick up your food while Nutrisystem delivers food to your door once a month.
Taste: On this level, there is really no comparison, while a few of the Nutrisystem options are tasty, I found Jenny Craig to be far superior in taste, presentation and appeal. I found Nutrisystems lunch offerings to be of very poor quality, tuna is the cheapest available and all the "pasta" type lunches taste the same. Many of the nutrisystem dinners included kidney beans even the lasagna, while JC was more "real" food. With Jenny Craig, the turkey burgers and sandwich options were much better in my opinion. I had no difficulty sticking strictly with Jenny Craig, but I got bored (and felt denied) with Nutrisystem.
Support: Nutrisystem sends you literature with your monthly delivery and you apparently can contact them on-line. With Jenny Craig, you go into the center weekly and you weigh-in... big difference. While I only spent a few minutes with the councilor weekly by choice, they did offer good advice and support that was appreciated. Also, weighing in front of another person is more motivating. I find the Jenny Craig system superior.
Results: I lost 27 lbs. with Jenny Craig over a three month period and I think it's because I enjoyed the program and the food. I never had the urge to "cheat" and excercised more because activity is reported to your councillor. I lost 18lbs. over the course of three months with Nutrisystem and I always felt "denied" while doing this program. I also didn't have the same feeling of wellbeing with Nutrisystem vs Jenny Craig as, in my opinion it's not as nutritionally complete with vitamins and minerals.
Conclusion: I have no dog in this fight, this is just my own personal experience with both programs. I used Nutrisystem first and felt starved and regained the weight over the course of 8 months. I then tried Jenny Craig and haven't regained the weight over the course of 2.5 years. So in my personal opinion, I would definately (and have to all my friends) recommend Jenny Craig. I would not recommend Nutrisystem. Good luck with whatever you decide