below is a list of all the characteristics, skills and tier 1 talents that a given specialty has 2 aptitudes for. numbers in brackets show how many of each they get.
Heavy Gunner
(1/1/4)
Toughness
Scrutiny
Double Team, Iron Jaw, Resistance, Sound Constitution
Medic
(2/12/6)
Perception, Intelligence
Awareness, Commerce, 3 Lores, Linguistics, Logic, Medicae, Navigate, Scrutiny, Survival, Trade
Blind Fighting, Combat Sense, Heightened Senses, Light Sleeper, Meditation, Total Recall
Operator
(0/8/6)
Acrobatics, Linguistics, Medicae, Navigate,Operate, Security, Stealth, Tech Use
Catfall, Leap Up, Lightning Reflexes, Rapid Reload, Technical Knock, Weapon Tech
Sergeant
(1/4/6)
Toughness
Athletics, Command, Parry, Scrutiny
Air of Authority, Disarm, Iron Jaw, Radiant Presence, Resistance, Sound Constitution
Weapon Specialist
(2/3/8)
Ballistic Skill, Agility
Acrobatics, Operate, Stealth
Ambidextrouse, Catfall, Deadeye Shot, Leap Up, Lightning Reflexes, Quick Draw, Rapid Reload, Weapon Training
Commissar
(1/3/3)
Agility
Acrobatics, Athletics, Scrutiny,
Leap Up, Quick Draw, Sure Strike Weapon Training
Ministorium Priest
(1/8/6)
Fellowship
Athletics, Charm, Command, Deceive, Inquiry, Interrogation, Intimidate, Scrutiny
Air of Authority, Disturbing Voice, Enemy, Mimic, Peer, Radiant Presence
Ogryn
(3/2/10)
Toughness, Weapon Skill, Strength
Athletics, Parry
Ambidextrous, Beserk Charge, Double Team, Frenzy, Iron Jaw, Resistance, Sound Constitution, Street Fighting, Take Down, Unarmed warrior
Ratling
(4/9/16)
Fellowship, Agility, Ballistic Skill, Perception
Acrobatics, Awareness, Charm, Deceive, Inquiry, Operate, Scrutiny, Stealth, Survival
Blind Fighting, Catfall, Combat Sense, Deadeye Shot, Disturbing Voice, Enemy, Heightened Senses, Leap Up, Light Sleeper, Lightning Reflexes, Mimic, Peer, Quick Draw, Rapid Reload, Unremarkable, Weapon Training
Psyker
(2/10/4)
Willpower, Intelligence
Athletics, Commerce, 3 Lores, Linquistics, Logic, Psyniscience, Scrutiny, Trade
Meditation, Total Recall, Unremarkable, Warp Sense
Stormtrooper
(1/3/7)
Weapon Skill
Acrobatics, Operate, Stealth
Catfall, Double Team, Leap Up, Lightning Reflexes, Street Fighting, Take Down, Unarmed Warrior
what is immediately apparent, is that it's cheap to be a ratling, and heavy gunners are a bit shafted. its by no means a hard and fast guide, but considering you have 4 stages of skills and characteristics to buy, its not a case of starting fast/slow.
im still not sold on Stormtroopers WS aptitude, making them into ogryn-lites. also ratlings have lots of aptitudes that mesh perfectly.