When visiting NYC, midtown seems to be the preferred location.  

to stay in my spare bedroom.

...also one of the more saturated spots probably (just like Midtown) but for good reason. Another option would be the Georgetown-Foggy Bottom area.

Crystal City, which is just across the river in Virginia, has many hotels with less expensive room rates, especially when compared to DuPont Circle. There is Metro access and parking is not hard to find.  

I'm not sure why Dupont Circle gets so many responses to this question, which is asked often on this board (no slight intended to you, it's a good question). There are decent 4-star hotels throughout Downtown DC that are within 4-5 blocks of the red/orange/blue/yellow lines. Any of these will suit your purposes. If you like dining in good restaurants, closer to Penn Quarter/Verizon Center/Chinatown may make you happier than Dupont Circle.

so if you choose a location with metro access you are often choosing a location without good parking for the drive and park guys.....

.., and gentlemen love the location; especially if venturing out for cocktails, dinner, etc.  If gentlemen wish to drive, there are three parking garages within a few blocks of me.

I generally stay in the Arlington, VA. area and will be there again in October.