first most units are effected by doctrine buffs, that means a perhsing/m10/m18... is with hvap better then normal( 10 percent more damage ...)
how the armour behave against axis tanks? except few exceptions they do pretty the same as in vcoh. u fight a tiger not alone with one m10. NEVER. As allied player u search for the combo of mostly stickys/m10/atg to finish off heavy german armour.
riflemen with bars and its suppression are very effective in a lot of situations and are very well to combinate with smoke+flamers or just flamers.
Apart from what he said about HVAP, he's got it summed up pretty well - HVAP is a bit more complicated than simply 10% more damage.
Don't give Riflemen all three upgrades at once, specialise them. BAR's for full on AI duty, grenades for a cheap assault unit and Stickies to deter (Read: NOT hunt, DETER) enemy vehicles.
Rangers and Airborne are good but you have to realise what they can and cannot do. Thompson Rangers are very good AI, but are quite expensive and require either suppression or smoke to work to their best without loosing half the squad to kill one enemy. Bazooka Rangers will tear up LV's but can only scratch tanks if you know how to flank or distract. Airborne are brilliant AT but suck arse against infantry. All elite infantry works best with some form of healing.