Both.
Personally I never miss an Opportunity to stop in Canyon de Chelly - almost a religious place for me, if you are lucky and can get there in the off season when you go around almost totally alone and at peace it is just unique, so I never miss it when we are anywhere close. Mesa Verde is one of those places you have heard so much about you can only talk or think about it if you have been there.
So always Canyon de Chelly and if you have never been you need to go to Mesa Verde.
Couple of other places we will always try to drive by when we are in this corner of the world - Monument Valley - Mexican Hat -
Enjoy your trip, no wrong choices,
BOL,