I think the stock Notepad in Windows 10 is perfectly fine and speedy at least, I've never considered it too slow unless I open a huge file with word wrapping on.

Notepad2 is my all-time favorite though. It supports key features like line numbers and directionless search, but is much closer to stock than Notepad++. [0]

[0] https://www.flos-freeware.ch/notepad2.html