pretty much only Barewire/Krab from RIO, his videos are great. If you are transitioning from 6max, I especially recommend watching his series with sr against Educapoker and hhecklen, where he points out common mistakes by 6max players transitioning to HU.
Every other producer I've watched doesn't even come close to quality of Krab's videos. You might wanna try watching some Sauce's videos on HUNL as well, they are for sure great, but way above my comprehensive capabilities