I always felt like each background can be described as such in my opinion:

Earthborne/WarHero: Reformed
Earthborne/SoleSurvivor: Resourceful
Earthborne/Ruthless: A Thug
Spacer/WarHero: Prodigal Soldier
Spacer/SoleSurvivor: Resilient
Spacer/Ruthless: Spoiled
Colonist/WarHero: A beacon of hope
Colonist/SoleSurvivor: Unshaken
Colonist/Ruthless: Vengeful

I like Sole Survivor most because it gives Shepard an arc with the Thresher Maws, in the past they killed his unit, in Mass Effect 1 he kills tons of them with vehicle mounted heavy weapons, in Mass Effect 2 he takes one down on foot with his squad at his side, in Mass Effect 3 the mother of all Thresher Maws helps him take down a Reaper.

Ruthless/Spacer -"I didn't have much growing up. Only a loving family and a guaranteed military career to look forward to. Useless crap like that."
War Hero/Earthborn, Sole Survivor/Colonist: 💀

Colonist/Sole Survivor Shepard is perfect for not letting anyone die in the Suicide Mission of ME2. Since Shepard who has lost everyone twice would probly say to themselfs "I am not losing anyone. Not this time!"

Fine, fine, twist my arm, I'll play it again.

My shepherd is always a spacer because having a family a mother i speak too does more to inspire me to fight the monsters without becoming a monster then any tragic backstory ever did

there's a scene in ME2 where mordin tells shepherd that he can't fight to save the galaxy because the galaxy is too big but he can fight for his favorite nephew

“My name is Commander Shepherd, and this is my favorite Mass Effect video on the Internet.”

"You wanna play Mass Effect. Again. As you do."

I've never felt so rightly called out so quickly in any video before.

6:55 Damn, this hit deep. "You don't have to suffer to be valid. And you certainly don't have to suffer MORE to be MORE valid."

Spacer/Ruthless. I picture this as more of a Arcann story line. Ruthless Father that always judged his son as not good enough, forming him into a ruthless pile of hate. He was formed as weapon, not raised as a child with love. His Mother still talks to him because she regrets not getting invovled and still believes there is hope for him. He is Zuko.

I always play a Colonist/war hero. I like the idea that Shepard has always taken loosing quite hard because of what happened and will always fight like hell to defend anyone and everyone.

Earthborn/War Hero is Plastic Man. I started out a criminal, but now I've been given a second chance, and I'm gonna use it to save people with a smile!

To me, as funny as Spacer Ruthless can sound on the surface, that's actually Garrus. A C Sec legacy family. He was brought up around discipline and rules. But he developed focus on the end goal over all else. Even when Paragon Shepard influences him, he still reverts to his own instincts and goes Ruthless on Omega.

In fact, I would argue each companion in Mass Effect 1 can represent an archetype for each variant of a war hero or ruthless. Which adds further to your idea of Sole Survivor archetype being Shepard

Never considered or even roleplayed Colonist Ruthless Shepard as a vengeful xenophobe but rather as a person who got dealt a bad hand in life and has to overcome the bad rep he got on Torfan.

That stray "Wrex" at 2:12 was hilarious.

The repeating "Whatever it takes" at the beginning reminds me of the
"Fuck it we ball
Fuck it we ball
Fuck it we ball"

Earthborn is just your quintessential cinderella story. A literal street thug who breaks free from that life, overcomes adversity, and becomes something greater than they could have ever imagined. From Lv. 1 Crook to Lv. 100 Space Marine.

Colonist sole survivor Shepherd always felt right. One of the last survivors of his home planet and his unit makes his desperation to take the fight the Reapers all the more real. He already lost twice because he wasn’t prepared enough to fight, but against the reapers? He has time, he has resources, he has the men, if he can simply get his ducks in a row he can stop the Reapers and protect a family he couldn’t those two times. Alos Akuze and Mindoir always felt like they came back meanwhile things like the Skyline Blitz literally never registered with me.

This just occurred to me, my sister’s name is Talitha, and my mom chose it because it means little girl in Aramaic. It comes from a bible verse where Jesus goes to heal this guy’s daughter, but when he gets there, she’s already dead. Jesus says “talitha cumi”, meaning “little girl get up”, and she does. The quest giver tells Shepard he needs to save this woman, taken when she was a little girl, but when he gets there, she’s already decided she’s dead. Shepard talks her off the edge, and Talitha remembers her name. Man I love the writers of these games dude.

One aspect I really like about roleplaying Shepard’s background and Service History is subverting expectations.
For example a Spacer/War Hero Shepard (who is teed up to be Paragonest of Paragons) who lets the mining asteroid hostages die to prevent Balak from doing the same thing to another colony. As Garrus says in ME3 using the cold calculus of war
Or conversely a Colonist/Ruthless Shepard who saves the hostages, because as much as they hate Batarians; protecting the innocent is more important to them, even if that means risking a another similar attack down the line