If I'm looking for something in the city itself I find Boston International to be the best and most consistent. Their girls tend to be on the younger side (19 - 25). They are well organized, seem to screen their help well. I read a post from them recently that they get recent pics from every girl who shows up so you SHOULD be getting what you see on their website.
Flirt is also a solid group, although I've had some minor problems. I've shown up at the door and the girl is definitely NOT the girl in the pic or her performance was not what was advertised by the agency. However, when I called the agency about this they were always very willing to help me out and "make things right". The other side of the coin with Flirt is they also have a LOT of real hot women of varying ages and some of my ATF's work for them when they are in town.
If I'm going to be outside the city I prefer roomservicegirls. Jill runs a class act organization. Her rates are excellent and her girls are pretty consistently highly rated. Unfortunately, I just don't get to 'play' outside the city much anymore.
Aside from indies, I've worked, primarily, with three agencies in the area and have had great experiences with all three.
Boston International, as it's been said, fields younger ladies but the pictures are always accurate and the service provided as advertised. They also seem to treat their ladies well, or so the girls would have me believe. They also seem to bring along a good number of newbies (or professed newbies). It was funny (and hot) being greeted, at one point, by a girl wearing the exact same negligee that she was wearing in her pictures on the site. I would eventually learn that she'd acquired the lingerie at BI's suggestion since they felt the black lace set in her original photos was potentially "boring" (I wouldn't have gone so far as that, but the pink set she'd picked up was certainly not an eyesore).
Aphrodite caters to a more upscale demographic, but I've not had an encounter where the additional cost wasn't justified. The girls they advertise as 9s and 10s are priced as such and have all met expectations and then some. The girls who are 7s and 8s are also appropriately priced and, regardless of looks, always deliver as promised. I had a mind-blowing doubles experience with a pair of their girls last year that redefined my hobbying career. So very good. They also put their girls up both in and out of the city, which is convenient, and they have one of the best websites out there.
Boston Asian Dolls is another favorite that I've been working with for a few years now. They've gone through a couple name and location changes, but the MO has remained the same, which is comforting. The "geisha girl" experience to the uninitiated can be a bit stifling. If you go into the date with the intention of running the show and controlling the pace and agenda, you may not have a great time. But if you just allow yourself to be led, the girls are always eager and willing to cater to your needs. BAD have a system and, trust me, it works.
I've not yet worked with Flirt or City Girls, but I've heard good things for both. I submitted my application to RoomServiceGirls in this most recent open enrollment period. Haven't heard back, yet, but my fingers are crossed.