Isaac Clarke.
Because unlike the Gears, he's not a cartoon caricature. Soldiers do suffer shellshock midst deployment and PTSD in the aftermath, that I will not argue with, but from the get-go? GoW is built from the ground up to emphasize the toughness, the invulnerability, and the superiority of these super-soldiers.
...Isaac Clarke is just an engineer who never knew his father, who's mother sold his college tuition to Unitology to further her spiritual 'growth', and just wanted to make enough in his paygrade by the end of the day. He's not a space marine. His forte is digging through the guts of machinery and tech to fix inevitable breakdowns. Isaac is drawn into a terrifying conspiracy with the psuedo-undead, afflicted with worsening dementia, hallucinations, and burgeoning insanity. And often times, his worse enemies are not the Necromorphs, but men and women fanatically obsessed with an end-time instrumentality of 'becoming whole.' It's just him, what few allies he can muster, and whatever spit and glue weapons he can salvage.
Isaac all the way.