Currently, I have been into a couple mods lately, like Tinkers Construct, Applied Energistics 2, and some of the technology mods out there, simply because it is what I love. The tools in Yonkers Construct can give endless possibilities, and with PlusTiC, mods can encorperatr their materials into Tinkers Construct. Applied energistics, being a storage mod, just helps me a ton. But I can't forget about Veinminer. I almost can't play modded with out it.
I have been latley getting into a modpack called A Progressive Adventure, which you first have to enable the questing, but it is the kind of modpack that I enjoy for fun, with only a bit of drop in frames.