Myself I run just a few minor ones. ... Forest Friend (both)
Yay!
I have about a hundred or so, but I do not use them all with every character. The ones I use globally tend to be the smaller ones that only change small parts of the game. Like the Keychain mod. Many of them I make myself to fix things I do not like. Such as one I made to fix the leveling issues by giving larger bonuses for fewer skill increases, or to change the birthsigns to remove the once a day powers and replace them with either powers that can used repeatedly, but cost magicka and/or fatigue, or ones that are constant in effect. Dearest to me are they voice mods by BruceVayne. I just cannot play the game without hearing the voices of my beloved Imoen or Viconia coming from my characters.
The ones I activate or deactivate depending on the character tend to be ones that add an article of clothing or an item that character is going to use. For example, I took http://img.photobucket.com/albums/v90/subrosa_florens/oblivion/Aela01.jpg staff from a larger stave mod and made a stand-alone mod from it. I changed the coloring, and the enchantment, and made it the quest reward for the Mages Guild staff quest (if you choose the Frost staff). Since Aela is the only character who is going to use the staff, when I switch to another character I will deactivate it. Likewise, I made a small mod that makes her part-owner of
A Warlock's Luck in Bravil, so she can live there with Ungarion. But after her, I will turn that off too.