I like taking regulars.
And then I will raise and lower certain units, as I see fit. For example lowering some mere support troops ( like Jeeps or trucks ) to green, and upping my tanks platoon to vet as much as possible.
The problem with taking veteran or better troops, is that you are loosing numbers of man and ammunition, cause of the higher cost, you get lesser men. Taking greens OTOH, to get even more men, is really hard, cause green troops are somewhat hard to maneuver the way I want ( longer responsetime ).