Ok for the hard mode here is my build.
Veteran
Operative
Concentration toward a stealth gamplay to avoid overwhelming gunfire
Stealth 5 (ASAP!)
ASAP! at 5 you unlock awareness master plus you have basic evasion just in case
Pistol 15 (level 5 ASAP!)
The best weapon line of all IMHO. Get to level 5 ASAP for cover targeting. I also found chain shot to be highly efficient on boss fights once you can fire three times or more with Steel Core Rounds
SMG 3
Basic veteran ability. very litle use for it beside cover fire and at level 3 you already have a basic bullet storm option so no need for further investment.
Shotgun 3 (maybe 4)
Basic veteran ability. I do not use shotguns at all. If I was to use it maybe one more point might become usefull for the +3 damage, but otherwise no need really.
Assault Rifles 3 (or 10 maybe???)
This is the ONE skill where I could use help. So far I have been using mainly pistol and martial arts. On hard mode there might be an increase need for long range options. Probably worth investing extra points in if only for the quiet long range kills with subsonic bullets.
Sabotage 7
ASAP! from immunity to your gadget, to breaking and entering, basic binary invisibility and of course the life saving spy luck! this is IMHO essential to level almost immediately. Anything past 7 is probably overkill but up to there, the entire line is awesome and cheap!
Technical Aptitude 10 or 15
The entire line is incredible! at higher levels you can pack almost every gadget out there and your heals become insane. Not the highest priority, but defenetly worth leveling when points allow. Bring to ten if you want to specialize in martial arts instead.
Toughness 15 (level 10 ASAP)
On hard, toughness is a requisite. At least to level 10 for the Hard to kill ability. I personaly bump that one all the way to 15.
Martial Arts 10 (or 15 maybe???)
Ok. personaly I love that line. I would recommend bringing it up to 10. I have noticed that a lot of boss fights end up in close quarters so martial arts seems to be IMHO more valuable than any other weapon line with the exeption of pistol. The problem is that if you do not invest in that line, you will be completely ineffective. I left it at blank in my first playthrough and even a low level goon would mop the floor with me in direct melee. I leveled it to 10 the second time and I was feeling like Chuck Norris, cleaning up entire waves of NPCs in mere seconds.
Here it is.
I hope it proves valuable to some.
Feel free to give me feedback with suggestions.