Andy
You start out with him. Andy is a well balanced CO with a pretty good CO Power. He is good with all types of units and has no real weaknesses. CO Power: Hyper Repair. Hyper Repair restores two Hit Points to every one of your units. It also gives all of your units stronger attack power for the turn you used Hyper Repair.
Max
Max's main strategy is to strike fast and hard. He is the best CO with direct combat units, but his skills with long-distance weapons are pretty bad. CO Power: Max Force. Max Force boosts the attack power of all direct combat units. Direct combat units can only attack enemies from adjoining squares. For example, a Tank is a direct combat unit but Rockets are not. It also increases their movement slightly for that turn.
Sami
The third CO to join you is Sami. Her specialty is Infantry and Mech units. Her troops cover more ground and capture cities and bases faster than any other CO's units. CO Power: Double Time. Double Time increases the movement range of all her Infantry and Mech units for one turn.
Olaf
Olaf is unaffected by cold snows that slow other units down, but rain tends to give him a lot of trouble. He is not the smartest CO, but his troops are well rounded. CO Power: Blizzard. Blizzard causes a lot of snow to fall. Snow sharply reduces an enemy's movement while leaving Olaf's units unaffected, but it does not last long.
Grit
Grit is the mellowest of all the CO's, but do not be fooled by his low key manner. He is a sharpshooter with long-distance units, but his direct combat units have a low firepower rating. CO Power: Sniper. Sniper increases the range and power of Grit's indirect combat units. Since Grit's units already have an impressive range, Sniper makes them almost untouchable.
Eagle
The skies have always called for Eagle, and as a result, his air units are the best in the business. His naval units, however, are extremely weak. CO Power: Lighting Strike. Lighting Strike allows his units to attack two times in one turn. In the hands of an experienced player, a well-placed Lighting Strike can end a battle before it has begun.
Kanbei
The best-trained troops fight under Kanbei's banner, and their defensive ratings are the highest in the game. It costs extra credits to deploy Kanbei's units though. CO Power: Morale Boost. Morale Boost gives Kanbei's troops a burst of energy and increases each unit's offensive rating for a single turn.
Drake
A master of the seas, Drake employs the best naval units in the business. Drake's weakness is air combat -- his air force is widely regarded as little more than cannon fodder. CO Power: Tsunami. This attack creates a giant wave that takes 2 Hit Points from every enemy unit, including air units.
Sonja
Kanbei's daughter, Sonja, is an information junkie. Her units are average across the board, but they can see farther than any other CO's units. Enemies cannot see her unit's HP. CO Power: Enhanced Vision. When used, her CO Power will increase every unit, even letting you see what is in reefs and forests without having to be directly next to them.
Sturm
Not much is known about Sturm. CO Power: Meteor Strike. A giant meteor comes crashing down and takes every unit it lands on down to two HP.
Strum is not affected by the area, meaning that the land will not reduce his troops movement.
Sturm is a power house in many ways. His power homes in on the most amassed troops, depending on the cost of all the units in the area and if there on a building or a base. His power is very easy to trigger. Powers are increased by you being attacked or you attacking the opponent. When you are attacked, it increases more that if it were you that is attacking. It increases more depending on the unit's cost. When he powers up in campaign mode, his offense increases and defense drops. However, in other modes it is the opposite. Sturm's powers are average but his strength is his movement on terrain. He moves without worry of movement cost. His weakness is snow.