Hello.
I've been looking through the posts here but can't find in what order I should play the sagas. I guess Empire first but the rest?

Not sure which game in particular you're referring to, so I'll cover them all. For Disciples: Sacred Lands I don't recall the order one played the sagas in being particularly important. Empire is probably the easiest to start with from a gameplace perspective so I'd recommend just starting there then going with whatever race you feel like after that. For Disciples 2: Dark Prophecy the order again doesn't really matter; while the sagas overlap a little bit in their stories at the beginning each one pretty much ends up going in its own direction. However, for Disciples 2: Gallean's Return I'd recommend the following order: Legions, Hordes, Clans, Empire. While the stories told in each saga fit together nicely regardless of the order in which they're played, it fits together better chronologically in the order that I listed the sagas. Rise of the Elves only contains a single saga so there isn't much of a concern there.

Thank you. I've been playing Disciples 2: Rise of the Elves and now I know it doesn't really matter which saga I play first.

Rise of the elves throws a bit of a curveball, since although 5 sagas are listed only the elven saga is new to the expansion, the other four sagas are just the ones from Dark Prophecy.

Doesn't matter to me. I always play the latest edition of a game if possible because it is generally a better gaming experience with patches, tweaks and such things.
So the Rise of the Elves sagas it is for me. :)

**Watch out for this. If you play the original sagas using Rise of the Elves, you won't be able to import your level 10 heros to the high-level expansion campaigns.

Also note that the Elf campaign story takes place after the end of the Undead Expansion campaign.