I use 3 different labs, with the same results. Just recently recalibrated to 140cd/m2 and the prints are much closer. So which is right, and why? How do we arrive at these numbers, where do they come from? i.e why does NEC recommend 150 whereas Eye One recommends 120?
There are many variables involved in calibrating a monitor, and the manufacturer's recommended settings are a good starting point. However, the viewing environment is just as important and will affect the perceived brightness of your monitor. I suspect that if your prints come back consistently lighter than you expected, your monitor appears too dark. Perhaps your room light is not optimum. For example, if it is completely dark, the monitor will look much too bright, and if it is too light, the monitor will tend to wash out somewhat. You would then have to compensate for incorrect room light in order to get the monitor to appear right, causing a discrepancy in the brightness of your prints.
If you like to work in your current room lighting, than it would make sense to use the higher calibration point with the monitor. I bought a set of light-blocking window shades, and keep a small 5000K lamp on the desk for checking prints. It is far enough from the monitor so as not to cause reflections, and the low level of light that reaches the monitor allows me to work comfortably. I use a CRT, and have my setting at 88 rather than the recommended 90, as my prints had been coming out a bit too dark at 90cd/m2.