I've done both in the past. The views on 81 are much nicer than 95, plus much less risk of traffic going from Philadelphia through South of DC. Traffic always seems to just move more quickly. Google maps said 81 was about an hour longer, but I think I made up for that with the additional speed I was able to carry down 81 to 77.

Be sure to time the trip so you're on 77 during the day. Views are phenomenal. You can see for miles on that descent.