As the topic says.

Personally, it's between Secret of Arcana and Companion's Insight. Basically infinite magicka and the ability to spam spells with no concerns for my companions. So very fun.

secret servant

I like bardic knowledge. It's nice that it's a lesser power, so you can use it whenever.

Companions Insight. None compare. I've been wanting that since I bought Skyrim.

Winds of Change - Companion's Insight for console version, Lover's Insight for PC version *mods fix friendly fire*

Epistolary Acumen - Dragonborn Force, because that's how Unrelenting Force should have actually been like.

Untold Legends - Black Market, my followers are pack mules and my healing spells restore stamina.

Sallow Regent - Seeker of Sorcery, because im a sorcerer.

Hidden Twilight - Mora's Boon, once a day elixer.

Filament and Filigree - Secret of Arcana, unlimited magic spam for 30 seconds = , still wouldn't be able to kill a dragon with the Deadly Dragon mod installed though, but it would bloody help.