Since you said you'll have a van that you must park, one thing to keep in mind is the difference in parking costs and overall tax rates at these RIs. DuPont is $25 per day (plus tax rate is about 14.5% - I'm not positive), Rosslyn is $12 per day (plus tax rate about 10.25%), and Pentagon City is $18 per day (plus tax rate is about 10.25%). Don't know if that's a consideration or not.

We stayed at Rosslyn in January, and the only negative at that time was that when we went to check in, there was no one at the front desk for about 20 minutes - it was empty. After that, it was a very pleasant stay, and I'd stay there again.

We were at DuPont a few years ago, and liked it as well. We enjoyed the location very much. Don't know how it is now.