Suppose you could only use ONE mod (excluding SKY UI, all the Unofficial Patches, and official DLC, SKSE, SSME, and ENBoost or ENB), what would that mod be, and why?

I know it would be a tough choice, considering we use many different mods for many different reasons, but think it would be interesting to hear what mods people value the most. Keep in mind you can only choose ONE mod, please none of ' this -or - that ' make your choice !

Myself, I think my ONE mod would probably be Vilja, because it just adds so much, quests, and so many different options and things to do in game.

http://www.nexusmods.com/skyrim/mods/17930/? - mainly because it it addresses the first thing I noticed in my first playthrough: unlootable containers.

Cutting Room Floor by Arthmoor probably. Expands on the Skyrim I love and fits in almost perfectly, also it enhances whatever character I make.

Vilja is also a good choice, but I don't think I'll ever replay the mod with another character.