I like all of them
They all have their unique look and feel.
Pretty much this. I can't say right off the bat which of them is my favorite. All are kinda good in my opinion. While a little remote, this isn't an issue except maybe for a Redoran, and even then Almsivi Intervention takes you to Ald'Ruhn where the other councilmen live. Those weird Hlaalu and hermit Telvanni people live here and there whatsoever; your location ain't that weird.
Also, the fact that especially Tel Uvirith is kind of small is just realism, I think. The other towers have been up for hundreds of years, so they have evolved into settlements already. People have had time to move there and stay there. This is not the case with Uvirith, which is small for this particular reason, I think. The tower itself is cool. So are the Redoran and Hlaalu manors though, especially Redoran.
Mmh. Just can't decide. None is clearly better or worse than the others. I, too, like the terrain the most near the Hlaalu stronghold. Actually it's either swamp or green, depending on which side you climb down.
Beats the barren wastelands in Uvirith's Grave and Bal Isra. Though, a true Telvanni couldn't care less, I think.
I've even gotten into every house's philosophy with at least one character, so, I can't name a favorite even by thinking what my favorite house would be. I just can't decide, you know. :/
Remoteness
+ Telvanni
+ Hlaalu
- Redoran
Terrain
+ Hlaalu
+ Telvanni (they don't care how it looks outside)
- Redoran
Special feel
+ Hlaalu
+ Redoran
+ Telvanni
NPCs
+ Redoran
+ Hlaalu
- Telvanni (those stairs to the other peoples' house are horrible, and the dwemer animunculi inside the tower is always in the way)
So, uh, Hlaalu, even though I actually care of them the least at the moment?