Getting a great deal at Nine Zero ($200/night), but concerned about the location. FS has a better location but is $$$$. How is the area around Nine Zero, can it compete with Back Bay?

The area around Nine Zero is fine - it is not far from the Common (block at most). FS isn't really Back Bay, it's in the theater district, but right across from another side of the Common, only a few blocks away from Nine Zero. You won't be at a huge disadvantage if you take Nine Zero, and it is a nice little hotel with a pretty darn good restaurant. I actually prefer the wine list at Spire to the one at Aujord'hui - the restaurant at the Four Seasons - as it is more accessible (i.e., more cheaper wines).

Is there something in particular you hope to be near?

I agree, go with Nine Zero. The location is good, Spire is excellent and $200/night is a great deal.

Dowtown Boston is small. Go with the Hotel you want and don't worry about location. Nine Zero is only about a pleasant 10 minute walk across the park from FS.

Nine Zero has great rooms, not huge but comfortable with cool modern decor and the bathrooms are lovely.

The cocktail bar serves excellent mixed drinks.

I have stayed at both hotels and I definitely prefer Nine Zero.

another vote for Nine Zero with a good rate.
We've had several excellent meals at the Spire restaurant and as someone mentioned, not far from FS and close to the Common, etc.