This needs to be a tournament. Frankotank, would you mind if I made it a tournament? (Or you can run it.)
My top all time cereals are:
Cracklin' Oat Bran - great out of the box or with milk, but perhaps the most unhealthy adult cereal ever
Cap'n Crunch with Crunchberries - great mostly out of the box, but good with milk as well.
Apple Cinnamon Cheerios - great mostly out of the box, but good with milk as well.
Honey Bunches of Oats (classic flavor) - great with milk, soso out of the box.
Raisin Bran - great only with milk, not very good out of the box.
As a kid and teenager I loved Fruity Pebbles and Frosted Flakes, but I haven't had either of them in years. I'm not sure they would translate to adult tastes.
My ancestors fought cave bears so I could make this post.