Oatmeal is a much better choice. Special K has less than 1 gram of fibre per serving, I believe = not good.
Like Grammaton said, don't get the instant oatmeal in the packets - they are full of sugar. I use regular oats and it takes about 4 minutes on the stove; the microwave is faster, but I prefer the creamier texture cooked on the stove. I add 1T ground flax, 1/2 chopped apple, and some cinnamon.