Should I get a Surface Laptop 2 or Surface Pro 6 for development?

For development? None of them. There are tons of notebooks that are better suited for development

A used thinkpad t440p

Not sure about the hardware but I've got a surface 3 pro running Kubuntu, do you want to use windows on it or doesn't it matter?

@linuxxx Windows 10, maybe dual boot

It really depends on the configuration you want and if you want to use on your lap.

A Dell XPS13. It's a fucking workhorse! (but without the fucking, I'm not a barbarian)

@FilipeRamalho Is the Surface Pro not very comfortable typing on your lap?

@ModernShoe A bit, but the Surface Laptop has a much better lapability.
https://youtu.be/it4n-EbC7Vs

But on the other hand the Surface Pro 6 has a more versatile Design and the touch screen is more useable

Do you want a tablet and a laptop
-> Surface Pro
You don‘t care for the tablet features
-> Surface Laptop

surface has 1/10 repair ability. And has thermal issues... is touch screen part of development?

I second the Dell XPS. It’s lightweight with a really impressive build quality and battery life.

Which ever you buy, remember this -

You need enough pizza and Diet Coke to stick in your refrigerator, a cheap PC to work on, and the dedication to go through with it.
~ John Carmack