First off do you have a personal connection to one of these tartans? I want the Black Stewart as my mom is a Stewart, for example.

If you have no connection to either than it comes down to esthetics, and as far as that goes IMHO I really like the Black Stewart. The MacDonald Ancient is very nice as well and as you already have the Douglas Grey, that makes it even more complicated.

I would have to say think about it in light of the accessories you have and if you think one of these would go better with what you have go for it first and put the other on the waiting list.