Number 1: The Rise of Fenris
Buy this firstAdds: An 8-game story campaign you can reset, plus 11 modules (including a co-op mode) to mix into normal games.
Fixes: Keeps the game fresh for groups who have played base Scythe a lot.
The one to buy first for most groups. Play the campaign, then keep using the modules.
Usually a better fit for a different kind of group — still fine if it sounds fun.