There are quite a few calorie counters here who've done a remarkable job with weight loss. If it's something you feel that you can do for the rest of your life (maintaining looks just like weight loss--we're in it for the long haul), then you might give that a try. If you have 100 lbs. to lose, however, I would go more with eating 1800 calories to start, then moving that down as you lose. Starting out at 1200 calories often leads to burnout and binging, IMHO.
Weight Watchers has a great reputation and has done a lot of research into weight loss. Their points system has taken all the guesswork out of calorie counting and making sure you get enough fiber and nutrients. Again, it's got to be something you can live with for the rest of your life.
Women who behave rarely make history.