I know that space engineers is not being sold on GOG, but anyway what do you say?

Do you like humour or serious game?
If you like humour then get KSP.
Isn't SE is still in early access?

I've never even heard of Space Engineers and all I've played of Kerbal is the demo and I know this answer without a second of hesitation!

Kerbals all the way!

KSP - Rocket simulator 20xx
Space Engineers - Minecraft in Space

I've played Space Engineers, it's ok. I have not played KSP, but from all the let's play videos I've watched on it I would go with KSP first ;)

Either way, have fun with the one you pick :)

Can it be an inclusive or?

It does say "or", not "xor".

Isn't SE made by those Miner Wars guys? I've had bad experiences with them, so personally I'd be avoiding SE for that reason.

Haven't played any of them but if I had to choose I'd go with the Kerbal Space Programmmmm.