DD 3515 or Sundown X 12 which one would you choose?

So I have a guy wanting to trade me a DD 3515 for my idmax 12 " that I don't even use anymore. Which would most of you guys prefer running off an soundqubed 1200d 1 ohm amp? I know one is a 12 and one is a 15 but I'm just seeing which would give the most output...I love lows as well. Trunk space is not an issue. I have an suv and think I could get away with a 4cuft enclosure at most with the dd 15. If I keep the DD I'll just sell the sundown x 12. Any input or opinions are welcome. Thanks guys