Main differences:
Mobility- Raven have greater deployment mobility for infantry, But Scars have good deployment for any unit (infantry, bikes, vehicles).
Assault: Scars have more that enable making successful charges and are stronger against anything turn 3 onwards. Raven are stronger only against character from turn 2.
Defense: Raven have better general defense. Scars rely on vehicles, or being in assault, for defense.
I think in general, Raven are close range shooters with opportunistic assaults. Scars are semi mechanised assaulters that still heavily rely on early game shooting. Neither one is really a dedicated assault army, but do happily match their background.