I would agree with the previous posters about nominating Wanderlust Reloaded
. Personally, I love it because I'm a builder/decorator stlye player and it offers endless possibilities for me and my ilk. There really is something for every type - magic lovers, machinists, explorers, hoarders, etc etc. The mods included are well integrated with the environment (BoP) and also with other mods.
What makes it unique? It's a pack that single players and servers alike can run and enjoy long term. There are interesting quests and tons of items to search for and acquire. The modpack creator has carefully tweaked the balance of foodstuffs, ores, items etc so that the pack isn't able to be finished in an hour, but at the same time isn't so crazy difficult that it makes you not want to play
Additionally it has a great variety of mods, and not just the big standard ones. There are some smaller lesser known mods included that really make the pack fun and add great gameplay. Finally the creator is open to suggestions, explains their decisions, and is responsive to issues/bugs. Highly recommended!