What about weapons? Theres so many early on.
Pistols. Good pistol for the rookies - Beretta (average accu with lowest TU-cost for
snat shooting). It's usable till you research BlackOps pistol. Default Magnum is not bad for the beginning (against big targets with low armor and high HP). BlackOps pistol is the best. On mid-range combat its more effective than most of rifles, except UAC rifle.
SMGs. As for me I don't use most of them. Well, if you'll be lucky you can obtain P90 - it is the best (ignores 20% of armor).
Rifles. All of them which use 5,57 caliber bullets - ignores 10% of armor.
Sniper rifles. Well, it's simple - use the most damageable, but remember about accuracy modificator (give them only to that soldiers who have accuracy 80 or higher)
Chainguns. Well, as for me I don't use them except Minigun - it's useful on high populated maps (cult outposts/bases/HQs, Apocalypse).