This is the list I used for my Non-Brony friends who are interested but planning on watching the full show. What I've done was break the show into story arks. that way they can narrow down the episodes to watch.
This is what I got so far.
If you got more to add let me know.
Grand Galloping Gala
S1 E03: The Ticket Master
S1 E14: Suited for Success
S1 E26: The Best Night Ever
[bonus]
S5 E07: Make New Friends But Keep Discord
The Crusade for the Cutie Mark
S1 E12: Call of the Cutie
S1 E18: The Show Stoppers
S2 E06: The Cutie Pox
S3 E04: One Bad Apple
S4 E14: Twilight Time
S5 E06: Appleoosa's Most Wanted
S5 E18: Crusaders of the Lost Mark
S6 E4: On Your Marks[bonus]
S1 E17: Stare Master
S2 E23: Ponyville Confidential
S4 E05: Flight to the Finish
The CMC Nightmare Trilogy
[For Context]
(Search)
CutieMark Crusaders-----
S3 E06: Sleepless in Ponyville
S4 E19: For Whom the Sweetie Belle Toils
S5 E04: Bloom & Gloom
FlutterShy’s Struggle
S1 E07 :Dragonshy
S1 E17: Stare Master
S2 E19: Putting Your Hoof Down
S2 E22: Hurricane Fluttershy
S4 E14: Filli Vanilli
[special] S4 E16: It Ain't Easy Being Breezies
Rainbow’s Strive to be a WonderBolt
S1 E06: Sonic Rainboom
S3 E07: Wonderbolts Academy
S4 E10: Rainbow Falls
S4 E21: Testing, Testing, 1, 2, 3
S5 E15: Rarity Investigates!
S6 E07: Newbie Dash
Rarity’s Strive for Fashion
S1 E14: Suited for Success
S1 E19: A Dog and Pony Show (small part but important)
S2 E09: Sweet and Elite
S4 E08: Rarity Takes Manehattan
S4 E19: For Whom the Sweetie Belle Toils
S5 E14: Canterlot Boutique
S6 E03: The Gift of the Maud Pie
S6 E09: The Saddle Row Review
[bonus]
S5 E15: Rarity Investigates!
“Dear Princess Celestia” saga
Season 1 : (Weekly)
Season 2 : (Post-“Lesson Zero)
( officially Ends in season three)
The Equestrian Games
S3 E12: Games Ponies Play
S4 E05: Flight to the Finish
S4 E10: Rainbow Falls
S4 E24: Equestria Games
[For Context]
S3 E02: The Crystal Empire, Pt. 2[bonus]
S3 E11: Just for Sidekicks
Princess Twilight/The “Box”
(Twilight’s NEXT Magic Studies) More or less all of Season 3--------
S3 E13: Magical Mystery Cure
S4 E01: Princess Twilight Sparkle, Pt. 1
S4 E02: Princess Twilight Sparkle, Pt. 2
S4 E08: Rarity Takes Manehattan
S4 E10: Rainbow Falls
S4 E12: Pinkie Pride
S4 E16: It Ain't Easy Being Breezies
S4 E20: Leap of Faith
S4 E25: Twilight's Kingdom, Pt. 1
S4 E26: Twilight's Kingdom, Pt. 2
[bonus]
S2 E20: It's About Time[special]
S5 E03: Castle Sweet Castle
“Cutie Mark Map”
[special]
S1 E16: Sonic Rainboom
S1 E12: Call of the Cutie
[For Context]
S1 E01: Friendship is Magic, Pt. 1
S1 E02: Friendship is Magic, Pt. 2
S2 E01: Return of Harmony, Pt. 1
S2 E02: Return of Harmony, Pt. 2
S2 E15: Super Speedy Cider Squeezy 6000
S2 E25: A Canterlot Wedding, Pt. 1
S2 E26: A Canterlot Wedding, Pt. 2
S3 E01: The Crystal Empire, Pt. 1
S3 E02: The Crystal Empire, Pt. 2
S4 E25: Twilight's Kingdom, Pt. 1
S4 E26: Twilight's Kingdom, Pt. 2
(Search)
Zecora
Maud
Gilda
-------
S5 E01: The Cutie Map, Pt. 1
S5 E02: The Cutie Map, Pt. 2
S5 E08: The Lost Treasure of Griffonstone
S5 E12: Amending Fences (?)
S5 E16: Made in Manehattan
S5 E22: What About Discord? (?)
S5 E23: The Hooffields and McColts
S5 E25: The Cutie Re-Mark, Pt. 1
S5 E26: The Cutie Re-Mark, Pt. 2
-------
[bonus]
S1 E23: The Cutie Mark Chronicles
S5 E17: Brotherhooves Social
Starlight's character arc
The Cutie Map Part 1
The Cutie Map Part 2
The Cutie Re-Mark Part 1
The Cutie Re-Mark Part 2
The Crystalling Part 1
The Crystalling Part 2
No Second Prances