Hi
The trials and tribulations of diets and how to stick to them is hard. My advise would be to chuck the Atkins and go with a plan you can stick to. If you can't even go a full week without "blowing" a diet, it would be nearly impossible to go a lifetime on that eating plan. There are brownies around every corner to trip you up.
Try counting calories. This gives you limitless possibilites on what you can eat. You can have a brownie now and then and not worry about it. You can eat all the food you love within reasonable amounts.
Eating less than you burn will work every time for every person.
When chosing an eating plan for life, be honest with yourself. How easy is the plan you choose going to be to stick to a month or year from now? You will have to limit what you eat for the rest of your life because if you are left up to your own devises, you will over-eat as you've always done and gain it all back.
To me, it sounds quite a bit better to eat what you like to eat within reason. A little self control with portions is all you'd need to do.
Don't give up on yourself or you'll just stay where you are or get bigger. Don't overwhelm yourself with rules right out of the gate. Too many "I can't haves" will doom any diet. Today do just one thing: start eating the serving size of every food you eat. Check the packages of food, serving sizes are listed on every package. Do this for awhile, see how it goes.
I lost 35 pounds by eating 1200 calories a day. I've been maintaining at right around 121-123 now for about 7 months. I think what I did was drastic. Looking back, I could have lost all the weight just by eating the serving size of every food. That is how I'm maintaining. Although I do still count calories, I can go for days and not count and not gain because I know that if I eat the serving size that it's nearly impossible to over-eat.
Whatever you decide to do. Good luck to you. Don't give up. Try looking at a long term goal. I lost the first 25 lbs in 5 months. By Christmas you could be down 25 lbs or more. It is within your reach.