I work in SF on a regular basis and stay in hotels quite a bit usually targeting the $100-$150/night. Carlton just completed a $5mil renovation and the rooms are very clean. One annoying thing is that there is free internet in the lobby, but they charge you extra from internet in the rooms. If you get a room that "includes internet" you'll simply be paying $10-$15 more per day for the same room without internet.
It's pretty annoying especially how inexpensive it is with wifi to get the rooms wired.
some comparables i've stayed in, Diva, kensington park, commodore, union square hotel, pickwick. Carlton is definitely cleaner and nicer than any of these, which are in the similar price range.
location is great as well where you're a quick walk to union sq (10 min) but also can hit polk st and other parts of the city away from union sq.
get there.
more