The Dawnguard Questline from the Dawnguard DLC, is definitely one of my favorites. I always enjoy The Forsworn Conspiracy which you pick up immediately after entering Markarth. Daedric Quest wise: Peryite's (Picked up at Peryite's Shrine) is actually my favorite of them all, which I still find shocking. Lastly, my favorite Dragonborn DLC questline is probably The Final Descent at the Raven Rock Mine. I've only done it once so far, and for my current character, and I find it to be extremely entertaining.
My favorites are College of Winterhold, Main Quest, Dragonborn, and just about any quest involving running through giant dwarven ruins.
I just love delving into abandoned, massive dungeons filled with falmer and animonculi. They feel dark, cold, and lonely. They leave me paranoid, especially when I role play. I pack my food and supplies, grab a party, and dive in grabbing whatever I came for and anything light weight and valuable to sell for profit. When I find an area to break camp, I summon my atronachs to stand guard outside, set rune traps, and sleep in shifts with my followers.