What are the best add-ons?

[Gothyoba]

I would recommend Dwarvish Kingdom (campaign), Story of the Wose (campaign) and Reign of the Lords (era).

[Atreides]

Era of Magic, Dominus Maps, Ally Village mod, Cancel Goto If Attacked mod, Revolution & Civil War mod, Innana Maps, Anything by Bob the Mighty (although they are too hard), Afterlife, Random Recruit mod. And yes, I have yet to find a campaign I like. : ) Oh and well most Eras, can't list them all without missing some. So I'll just say all eras.