Andy, also known as the mechanical boy wonder, is an Orange Star CO and the main protagonist of the first two Advance Wars games. He doesn't have any obvious weaknesses and is good with land, sea and air units.
When playing as Andy, make sure to play very safe, avoiding unnecessary damage to troops and retreating damaged ones to heal. You can get an easy unit advantage just by healing some near-death units to at least 6 HP with a well-timed Hyper Upgrade, but only if your forces don't get wrecked before he can use it.
It is often best to just wait for Hyper Upgrade to be ready, as his Hyper Repair, while decent, is overpriced at 3 stars; use the CO Power only if a unit really needs that 2 HP heal, or you're playing versus Sasha.
Hyper Upgrade's 5 HP heal is enough to reverse or even completely nullify first strikes on his units, so feel free to play more aggresively when the power bar is full, or even if you just think the power bar will be filled from enemy counterattacks next turn.
Another thing to note when playing as Andy is that even though he has no obvious day-to-day advantages, he can gain relative advantages when facing specialists in the battlefield. That means he gains an indirect-unit advantage over Max, Air and Naval unit advantages over Jess, and so on. It can prove beneficial to play to your opponent's weaknesses as Andy.
Due to the nature of Andy's powers, expensive units like Bombers or MD tanks are especially effective (sturdy, to be more precise) if he gets to afford them.