My favorite modpack is definitely the old Tekkit for Minecraft 1.5. I’ve probably spent more hours in Tekkit than any other Minecraft version or modpack.
As for a mod, I wouldn’t say this is my favorite mod, but I want to recommend Chalk. It’s a very simple mod that adds a chalk item, which you can use to draw arrows on the ground. It’s very useful for marking your path when exploring open areas and cave systems.
Me and my friend are playing a Create modpack and just discovered Tetra for the first time. It adds so much wonderful complexity to the tools and weapons in the game. It’s honestly so much more streamlined then Tinkerer’s Construct.