I've eaten at both once. Most recent being the QVR. I think it's spoiled me, and I'll be shooting for that from now on. It makes sense to look at both sample menus and think about which would suit you more.
With the MDR you get fewer courses, but have choices to make regarding your dinner. It is also less expensive. With the QVR, you get more courses, but you are not actively choosing what you're being served, and it is more expensive.
When I went to the MDR, I ended up choosing a couple of items with upcharges, once I figured that in, I was basically spending what the QVR would cost, that's partially why I chose it for August.
The other reason why I went that route was that there is a lot of table side preparaton involved in the QVR, which I thought my DS would really enjoy, and since we were there celebrating his 18th birthday, I wanted it to be something extra-special.
Honestly, you can't go wrong with either one.