The friendship levels rank in this order:

• Stranger: 0-8400
• Acquaintance: 8400-16800
• Buddy: 16800-25200
• Friend: 25200-33600
• Good Friend: 33600-42000
• Best Friend: 42000-42999

Best Friend reputation levels with these NPCs have the associated achievements: Friend on the Farm and Friends on the Farm.
 
Don’t know what Dark Soil looks like? Here’s a picture:

 

The amounts listed below are without any guild perks. With guild perks (+10% reputation), 900 becomes 990, 540 becomes 594.

 

NPC	Blue Feather	Jade Cat	Lovely Apple	Marsh Lily	Ruby Shard
Chee Chee	900	540	540	540	540
Ella	540	900	540	540	540
Farmer Fung	540	540	540	900	540
Fish Fellreed	540	900	540	540	540
Gina Mudclaw	540	540	540	900	540
Haohan Mudclaw	540	540	540	540	900
Jogu the Drunk	540	540	900	540	540
Old Hillpaw	900	540	540	540	540
Sho	540	540	900	540	540
Tina Mudclaw	540	540	540	540	900

 
Along with the gifts from Dark Soil, you may give 5x crafted food once a day to each NPC (if you have the items in your bags, they appear as Daily Quests above the NPCs):

• Chee Chee – 5x Valley Stir Fry (Reef Octopus x5 and Wildfowl Breast x5)
  Chee Chee can be found either at Halfhill or at his home directly west of Halfhill (34.4, 46.8)
• Ella – 5x Shrimp Dumplings (Mantis Shrimp x5)
  Ella can be found at Halfhill or directly north of the road north of Stormstout Brewery (31.5, 58.1)
• Farmer Fung – 5x Wildfowl Roast (Wildfowl Breast x5)
  Farmer Fung can be found at Halfhill or at his field north-northwest of Halfhill (48.3, 33.8)
• Fish Fellreed – 5x Twin Fish Platter (Krasarang Paddlefish x10)
  Fish Fellreed can be found at Halfhill or at the pier northwest of Halfhill (41.6, 30.0)
• Gina Mudclaw – 5x Swirling Mist Soup (Jade Lungfish x5)
  Gina Mudclaw can be found at Halfhill.
• Haohan Mudclaw – 5x Charbroiled Tiger Steak (Raw Tiger Steak x5)
  Haohan Mudclaw can be found at Halfhill or his house northwest of Halfhill (44.6, 34.1)
• Jogu the Drunk – 5x Sauteed Carrots (Juicycrunch Carrot x10)
  Jogu can be found at Halfhill, south of the cooking trainers near the pond
• Old Hillpaw – 5x Braised Turtle (Raw Turtle Meat x5 and Juicycrunch Carrot x15)
  Old Hillpaw can be found at Halfhill or his house far west of Halfhill (31.0, 53.0)
• Sho – 5x Eternal Blossom Fish (Lungfish x5 and Striped Melon x15)
  Sho can be found at Halfhill or on the Hozen plateau far northwest of Halfhill (29.6, 30.6)
• Tina Mudclaw – 5x Fire Spirit Salmon (Emperor Salmon x5 and Scallions x15)
  Tina Mudclaw can be found at Halfhill or her house northwest of Halfhill (45, 33.8)

For each daily food gift, you will receive 1800 reputation (1980 with 10% Guild rep bonus).

Here’s what you get for getting “Best Friend” status with the NPCs.
 

NPC	Reward 1 (for Farm)	Reward 2 (items)
Chee Chee	Farm Sheep	Chee Chee’s Goodie Bag (cloth and leather)
Ella	Luna the Cat	Tree Seed Pack (tree blossom seeds)
Farmer Fung	Shaggy the Prize Yak	Enigma Seed
Fish Fellreed	Farm Pigs	Special Seed Pack (profession seeds)
Gina Mudclaw	Mailbox	Celebration Gift (fireworks)
Haohan Mudclaw	Miss Fifi the Mushan	Songbell Seeds
Jogu the Drunk	Free Crop Predictions	Secret Stash (booze)
Old Hillpaw	Farm Chickens	Straw Hat
Sho	Orange Tree	Red Cricket (pet)
Tina Mudclaw	Furniture	Food