I have an Athletic subscription, since I believe in supporting good journalism, but they are often not the first, since they only report when they have reliable info, their in-depth behind the scenes articles are unrivaled, Mitten, Whitwell and Ornstein all seem to have lots of inside sources.
if you want fast, but less reliable then Fabrizio Romano has you covered, that's his stuff basically, he tries to cover stuff fast, but is not entirely reliable with details, plus he promoted greenwood and sometimes steals exclusives form others, so up to you if you want to follow that.
SkySports also seems to be quite reliable since INEOS came in, seems like they managed to get a source inside United. They have been front runners for lots of transfer stories coming out.
There is also a whatsapp channel or whatever by the Athletic, haven't checked that out yet.