Medifast is a low carb, low glycemic, low fat, and low calorie diet designed for quick weight loss. You mix the products with water, and you eat 5 Medifast per day along with one Lean and Green meal.
Slimfast has twice as many calories when blended as instructed on the package, so you can't have as many per day, and may get hungry. It has more carbs, which can affect weight loss speed when compared to Medifast. The nutrients are different, too.
Slimfast is well suited for someone that just has a few pounds to lose. Medifast is designed for someone with a lot of weight to lose.
I've tried Medifast and agree that the soups are not good. I enjoyed the drink mixes, puddings, chai, and everything else.