Infantry: Attack, ATGM's are your tank killers, get some missile armed IFV's as well, some anti-air people are good as well
Helicopters: Anything with anti tank missiles and a gun, you need ones with loads of missiles like Havoc and Apache, use them at a distance so they don't get taken out by small arms.
Tanks: Pact, most are expendable and often have missiles so they are quite good at attacking, missile armed tanks are some of the best in the game, avoid lower ones they are too weak to be very useful apart for spam tactics
NATO: better at defence, position in cover to guard open ground, no missiles
but good armour, accuracy, good gun dmg, and nice armour or nice speed
Logistic: get the helo's, although they cannot enter woods they move faster and don't need to use roads
Support: I prefer gun armed anti air as it uses less resources, as far as arty goes big guns over missiles for me
Recon: I usually use an IFV rather than a dedicated recon, recon helicopters are good