As Miles said,
Justin Rhodes takes the lead with the great American farm tour. I should add his membership area - not the youtube part- is also recommended. The real deal is over there.
Richard Perkins is sharing a great wealth of information and experience through his youtube channel. He is known as the author of "Making small farms work" and through the movie "Gracie's Backyard". Refer to about farm efficiency, market garden, boilers and layers. He is currently sharing all of his 2017 season. I would recommend to watch it from the beginning, because he does not explain things couple of times (the videos are already pretty long, but worth to watch it). He also likes to take risks and try new things, but not like "heey lets try this and that and that one too". Calculates, discusses and then makes decision.
Richard Perkins - Ridgedale Farm
For urban farm - market garden, well it is obvious I think, Curtis Stone. 4-6 min long videos right to the point.
Curtis Stone
I would recommend one yard revolution channel. He puts forward some quality information. Season extension, misconceptions - misinformation, efficiency in city lot gardening and making most of little land. A video per week.
OYR Frugal & Sustainable Organic Gardening
Rob Bob from Australia. It is always fun to watch someone has nothing to do with your problems. Well at least mine. Aquaponics, wicking beds, root pounches, tropics and ginger! "Cheers folks!".
Rob Bob's Backyard Farm & Aquaponics
For Mediterranean garden, The Natural Farmer, long videos with very calm, slow talk. My climate, what can I say.
The Natural Farmer
Have Fun!