Reasonably speaking, you're rarely going to have a perfect 1-2-3 curve. For aggro, you just want to be using your mana as efficiently as possible. A 1-2-2&1, or a 1, 1&1, 3, or even a 1, 1&Tapland, 3 curve is completely reasonable. It's not ideal to miss a 1-drop but there are definitely hands...