Top 5 mission votes thread:
See this wiki:
https://wiki.thedarkmod.com/index.php?title=Mission_recommendation_discussions
I would say that all of Moonbo's missions are essential, all Kingsal missions, all Melan missions, all Grayman missions,
Goldwell's Accountant series and Northdale series,
The Painter's Wife, Behind Closed Doors, Iris, No Honor Among Thieves, Langhorne Lodge, Mandrasola, The Golden Skull, Sir Talbot's Collateral, Noble Affairs, Written in Stone, King of Diamonds, Down by the Riverside, A Score to Settle, Heart of Lone Salvation, Lords and Legacy, Swing, Patently Dangerous, King of the Mountain, Living Expenses, Flakebridge Monastery, Betrayal
Many would say all of Sotha's "Thomas Porter" missions, though these are very difficult / challenging so there is a little controversy about that.