Not all cereals are created equal. In the end it comes down to calorie consumption. You will notice Honey Bunches of Oats and Whole Grain Cheerios have about the same calories per serving but Honey Bunches of Oats is 3/4 of a cup and Whole Grain Cheerios is 1 cup... And Kix is 1 1/4 cups for the same calories. There are also some good Kashi and generic unsweetened puffed wheat and puffed corn cereals that come in at about 70 calories per cup which is less than any of the ones I mentioned. Really if you look at the labels, most cereals (even the sugary ones) all come in fairly close in calories. The serving size and the sugar content are a lot different for those same calories though.
I have a bowl of low sugar cereal every day just because it is easy and have lost 35 pounds with this in my diet. But the rest of the diet is crucial.
For people that are overweight, you can lose weight eating just about anything if you pay attention to calorie intake and try and get lots of variety in your diet. This means lots of fruits and vegetables, meats, good cereals... you can even do pasta like lasagna or even worse on occassion as long as you account for it in your calorie intake. The better you eat, the quicker the weight will come off... Unless you are looking to get to single digit (competition low) body fat percents, you can eat just about anything as long as you have a lot variety of good foods in your diet and you set a calorie limit and make sure you don't go over it.