In general, the tiers are supposed to be in three categories. Weapon upgrades (stopping power), weapon proficiencies (sleight of hand), and special abilities (dead silence), The idea was that you choose one of each.
Edit: sorry posted that wrong. Should be weapon proficiencies, special abilities, and extra equipment. Would this layout work? I dont think I missed anything or see any conflicts.
Tier 1: Steady Aim, Double Tap, Stopping Power, Sonic Boom, Armor Piercing, Venom, Sleight of Hand Tier 2: Second Chance, Lightweight, Objective, Scavenger, Dead Silence, Hardline, Commando, Hacker Tier 3: Tactical Mask, Sniper Gear (hunter), Hardwired, Combat Medic, Ballistic Vest, Stealth Gear, Flak Jacket, Gambler