I just completed a 4 night stay at the StR Bangkok and I have to say I thoroughly enjoyed it. The breakfast spread could have been slightly more varied (or offered more specialties to order) and the pool could have been a bit bigger, but other than that I was very very pleased with the hard product, general service standards and attitudes, and the location (directly connected to Ratchadamri BTS, one stop from Siam, and easy access to most other parts of Bangkok).
Of course, getting a BRG rate and an upgrade from a deluxe/grand deluxe room to a metropolitan suite didn't hurt in the slightest either.
For the money I don't think I've had a better stay in Bangkok!
Compared to what I've seen of the other *wood hotels in Bangkok I think it really comes down to your price point. There are many good value stays to be had at any budget, but at the top end as far as I can tell the only real options are the SGS and StR.