I don't have any content I'd label my favorite. It depends on my mood whether or not something is my absolute favorite, and it can change the very next month lol.
I love housing, overland, vet dungeons and arenas, and Tales of Tribute.
Housing is definitely on my to-do list. I've acquired nearly every house in the game on my main server in anticipation of the day when I finally get serious about crafting, buying, and placing furnishings in each of my houses, apartments, and rooms.
Housing, It brings out my creative side, somewhat like when I was model making. I enjoy realistic detail, so that is the way I go about housing. Pity it costs an arm and a leg. I also enjoy questing, I need to pay for my housing bent somehow.
I was really into the 30 minute bg queues but now my fave thing is to ride for 5 minutes towards a fight in Cyrodiil to dismount for battle and lose all my stamina as I dismount and die in 2 seconds (no stam). Logged off
I just hope that PvP side will get better to rejoin the fray, otherwise I will continue to go through my Steam single player collection of never played games.