If you need it done ASAP and either don't have the time to visit your local passport agency or don't live reasonably close to one, a service is probably your best option. If you do live reasonably close and can set aside a day to go there, then doing it yourself is (imo) the best option. Note that the former option also costs quite a bit more due to the service fees and (if applicable) overnight shipping costs involved.

If you're talking about just using the State Department's expedited service, then that's really up to you and 1) how quickly you need it and 2) how willing/able you are to go to your local agency and possibly stand around all day vs. shipping it off in the mail. If 2 weeks ain't quick enough for you, you have your answer.