In terms of performance there is negligible difference. So don't go for it just because of performance.
But for me if I am building a new rig I would still go for m.2 because of space and the lack of cables and additional 2.5' space saved for another storage device. m.2 can clean up clutter in your casing which is important for some people, especially in ITX casings.
It's like inserting a RAM into a slot. No hassle.