If I was to go by the most watched, then it honestly goes to the multiple sources who provide extended versions of the game's music, so there really isn't anyone to name in particular. But I find myself always listening to music from both FFXI and FFXIV all the time.
I don't really watch guides. When I was a budding player I used to watch dungeon guides from Miztech. She's quick to explain things, which is how I need it for it to register. For a laugh or two I would watch ZeplaHQ as I find her to be really funny when she's not being a drama queen. I watch Meoni just for his voice. That guy seriously needs to be in radio or some form of broadcasting that will get him more recognition.
Everyone else pretty much annoys the crap out of me. Mr. Happy, Work2Game (Chris and Brian), Larryazur. Nothing against them personally as they all seem to be stand up dudes, and they contribute a lot to the community. This just applies to youtubers in general. The majority of them can only talk for so long before I find myself wanting to listen to something else.