I would just echo what someone else said about really taking a look at the schedules. Not only may they be less frequent than you would hope during rush hour, they also get very sporadic on some lines later at night or in the middle of the day. In some instances, there may be two hour gaps between trains once rush hour is done. So if you anticipate that you may have some long nights at work, you may want to think about that since you would hate to just miss an 8 p.m. train for example and then have to wait until 10 p.m. for the next one. And the ones not on rush hour tend to stop at every stop making the trips extra long.

Good luck!