The Arch-Mage's Quarters in the College of Winterhold is pretty good. It has an indoor garden to harvest ingredients and an alchemy and enchantment table. The Companions guild is kind of meh. I guess it has the Skyforge and a pool of sword wielding travel companions. It also has a pretty good view of the surrounding area from the back courtyard. Those are the only two I've claimed so far.
Dark Brotherhood by far. It has a torture chamber where you can beat people up until they tell you where they've hidden money.
I guess I could buy another home since I seem to constantly have around 20k these days. Might as well own all the homes on at least one of my datas.
Selling potions will give you a lot of cash. I had about 38,000 gold saved up before I bought the pricey home in Solitude.
The House of Horrors in Markath. It's free. It's got plenty of storage space. It's got a hidden altar for Daedric worship. And it comes with it's own self-generating interior fog for ambiance...