If you can afford it, the standing rib is your best bet. Inside round works well also, but requires slow and moist cooking methods to give you something chewable. Be sure to choose at least USDA Choice if in the U.S. If you have a local meat processor that hanldes local beef, you can get Prime grade for a good price. Otherwise, it's hard to come by.
And remember, especially if you use the round, cut thin and against the grain.
For Christmas many people would choose the Prime rib. It's almost as tender as the tenderloin, but it has more flavor. The only drawback is that it can be very expensive, but that is less relevant for a holiday dinner. If you don't want to go that route then get a top loin roast. It's the cut of meat where shell steaks (NY/KC strip) come from. It's less tender and more flavorful than the rib meat. The shell steak is still much more palatable than anything that comes off the round or the sirloin, and it's rich enough for a holiday meal.