Defaulting to the slightly slower but more stable QR method?

[andreasnoack]

Created from #500 to have a place to discuss if we want to make this change. This issue is closely related to #426 and #375.

I think I'm in favor of switching to using QR as the default. Thoughts?

cc @nalimilan @palday

[palday]

I'm also in favor - it's not that much slower for most common cases and it would avoid a lot of misunderstanding.

[nalimilan]

I agree. Better use the method that works in cases that do in other languages by default. That's one of main changes to make in 2.0 IMO.