Hi Dave and welcome to the board,
There's some similarities and some major differences between Medifast and Optifast.
I'm not an expert on the history of Optifast either, but from what i've heard, they were the same program back a few years. Somehow, for some reason, they split and Medifast went onto further development and improvements. Optifast I believe (i could be wrong) stayed basically the same as back in the days you were on it. I'm guessing it was some kind of politics on the direction of the company, which also could be wrong. If there's anyone in the know, i'd really like to get the real scoop on this some day.
As for today, some major differences are:
Medifast is soy protein based - Optifast is whey protein based
As stated, Optifast is only available through a recognized clinic
Medifast has a much wider selection of products
Medifast also has the health management line of products - Coronary, Diabetes, Fit for Kids, Joint Health (which i use), Women's health etc...
Medifast started the "Take Shape for Life" distributorships which gives customers the support (often by people who have used and succeeded on the products) from folks like Terry and Nancy.
As stated several other places on this forum, and never enough, you should take advantage of the period during the weight loss stage of the program to educate yourself on what lifestyle and diet changes are needed to maintain your weight.
The diet is only the vehicle to get you to your goal. There's no doubt that the product works, but if you go back to what got you here in the 1st place, we all know what will happen.
Happy Shakin'
Unca