All these earth vs space marine/ ork treads got me thinking, what if a space marine chapter was against a planet that still had all the tech from the dark age of technology?
who do you think would win and why?

I believe the Space Marines would be killed, unless the DAoT world is a passive agri-world type place. STC Titan and full massive Knight Titan legions, power armoured AI Iron Men soldiers, STC machine constructing all the war materiel the planet could want, and efficient plasma weapons, and a fleet of brand new human naval vessels. The Space marines would be screwed.

My thoughts, essentially. The Space Marines are privvy to some of the most overpowered technology in any sci-fi setting, and even they're outdone by the DAoT.

The DAoT army would win for the simple fact that it can field equipment that the space marines haven't seen, in greater numbers. The bottom line is the space marines would be out gunned

:SPOILER:
In Scions of the Storm, the marines fight some AI robot thing-a-majigs, and they still win.
Remember the Marines have something no machine will ever have....stupidity, they just never know when to give up.
Your whole chapter just got wiped out by a huge angry Deamon?
Dont worry, your a Space Marine, charge that bitch, because Space Marines dont know the meaning of common sense

Well, although I disagree with the stupididty thing. Space Marines know when to fall back and what not.

However, Space Marine technology is inferior. Normally, I always side with the Emperor's Angels but...not this time. Their armour and skill just isn't gonna cut against the pure technological power of the DAoT.

Space Marines charge into un-winnable situations and dress it up as courage/honour.
But meh, we'll just agree to disagree ;)

That's a little thing called plot armour Kickback. Rushing into unwinnable situations doesn't net you a win.

Well, I disagree because they win plenty of those situations. Just because something seems impossible, doesn't mean it is.

However, completely off topic for this post!

But it seems clear...SM < DAoT

I'm going to have to say the Space Marines would win, assuming equal number of men.

The DAoT weapons were probably outstandingly advanced, even down to the grunt. But keep in mind what sort of opponents they were designed to face--humans. Even as the DAoT continued, actual fights between humanity and aliens were few and far between. Xenos were tolerated and non-aggression pacts forged.

The very idea of a 8 foot giant wearing tank-level armor and carrying crewed-support weapons like a normal man would a rifle would be shocking and inconceivable.

But even beyond that, it's the centuries of drills and live combat and the ferocity that would win the day, I think.

Plus it's sorta hard to gauge how much more advanced the DAoT people were. We have land raiders, for example. They're large and powerful, but not so far as to be overwhelmingly so against comparably sized machines. It may be my own bias, but I don't see the DAoT as some Utopian wonderland where a laspointer would be equivalent to a lance battery off a battleship. It seemed more of a time of reliability and ease of construction--perfect for a spreading empire built on worlds with very varied circumstances.