Can anyone tell me the best way to get from the Reagan airport to Rockville, Maryland on a friday night?
I'd take the metro if you don't have a lot of luggage. Friday night traffic in DC can be terrible, so you'd risk being stuck in traffic for longer than it takes to get there on the metro. You can take the metro to Rockville in about 40 mins and for $2.75.
Actual time on the train will be no less than *50* minutes--then you need to add platform waiting time (twice, since you need to change trains--with the Red Line wait possibly longer since not all trains go as far as Rockville).
If "Friday night" means during rush hour, that should minimize waiting time--but it will definitely mean a higher fare (up to $5.45). It will likely mean uncomfortably crowded trains and longer train time since they take longer to load and unload at each of the ~19 stations along your ride.
If "Friday night" means after rush hour--prepare for waiting time of up to 15 minutes twice in addition to 50 minutes of train time.
Bottom line--easily over an hour on Metro at any time, barring any "unusual" service delays for breakdowns and single-tracking...which are now anything but unusual, especially on the Red Line.
The other question to consider is your actual final destination. You state that you're going to "Rockville" and (in spite of my obvious bias), Metro may not be all that bad an option if your destination is walking distance to the Rockville Metro station (or White Flint, Twinbrook or Shady Grove, all of which serve what could be considered the general Rockville area). But if it isn't--add another connection, more fare and more waiting and transit time with the public transit options if you don't have someone picking you up at the station.
Metro is only the "best" option when you're strictly considering cost. You should be from the airport curb to your destination very comfortably in no more than an hour via taxi any time of day, but it will come at a fare of about $50. For one traveler, it may be worth the $40+ savings to put up with the inconvenience of mass transit--I definitely would. If there are three or four of you, the per-person mass transit cost starts adding up and Metro becomes that much less of a bargain.
If there's just one of you, SuperShuttle might be a good compromise for curb-to-destination comfort at about $30 per passenger--but it will be longer than the taxi as they need to assemble passengers, and they could be making detours to drop off other passengers before you.
Hope this helps--more info (time of day, # in party, actual final destination) will get you a more focused answer.
Take Metro. You don't even have to step outside like you would for a taxi, which would cost more than 900% more. Metro is right inside the airport, a smooth floor for your rolling luggage. Believe me you won't be missing anything by not seeing the outside of National Airport.Edited: 10:26 pm, February 28, 2013