Multi-grain cheerios are certainly a better choice than many of the dry cereals out there! They have fiber, not a huge amount of sugar. They are a little high in sodium, but frankly, I'd eat them!
I eat regular cheerios several mornings a week. They do after all, have oats.
I measure out a cup, add 1% milk, an oz of walnuts and usually fruit (berries, peaches, etc) Fills me up nicely.
You'll have to read labels to find a really good cereal. You might try try the natural foods section of your grocery for some higher fiber/whole grain stuff. I know that WW's Core program allows only shredded wheat and puffed wheat or rice, and some whole grain hot cereals. Most cold cereals have lots of sugar and/or sodium, and some have as much sugar as a candy bar.