I really like Honeyside and Vlindrel Hall. Honeyside is nice, though could use a few more display options. The mannequins are also usually breathing and staring at me. Vlindrel Hall is awesome and has great view of Markarth.
My LEAST favorite is Proudspire. Proudspire Manor I really wanted to like, it was my second house purchase after breezehome, but its just too glitchy. Cluttered, no display cases, and very odd placement of items. First, when i fully upgraded it, the wooden rickety chairs and new fancy chairs were fully morphed into eachother. It seems like the game forgot to remove the old ones before putting new ones. Its stuck like that, even doing everything in a different order didnt help. After 4 hours of reloading, pruchasing in different orders and different times, the chairs in the house still just blended into a mess. The basemant wall flickers, and the bedroom wall's corners flicker too. The chest in front of the bed is just stupid looking, why point towards bed? I have latest update to 360 version, and this may very well be the worst house in my opinion (if anyone has solution for them blended chairs, please share).
Breezehome and Hjerim are both decent in their own rights, though if i had to rank the houses (best to worst) , it would be Honeyside-tie-Vlindrel Hall, Hjerim, Breezehome, and then Proudspire Manor.
Now what are your favorite houses in skyrim? What ones do you regret buying?