As previously mentioned, since the Capital Hilton is really close to a Metro Stop, it is very easy to get to all the tourist attractions.
However I found the Hilton Garden Inn to be located in a more of a "touristy" region, and a little safer.
You can take the MARC train / Amtrak into Washinton DC instead of a taxi. A taxi runs about $60 each way, and I believe the train is appreciably less, especially if you purchase a round trip ticket.