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.
i like to keep it vanilla, by which i mean i want to be able to still play on vanilla servers. so my favourite mods are interactic, visuality, smooth swapping and others of this nature. making the game look better while keeping the gameplay unaffected