I don't know how must park ski insight you will get from this forum, but a few of us still have spines and knees healthy enough to prefer that part of the mountain.
I first want to ask you, What do you plan to do with your twins? If you plan to land or ride switch, spin your airs, or ride the pipe, then a twin is the way to go. My brother and I have been riding Concepts (180's)for a season. After about 5-7 days of heavy use (big airs and some hard landings) both pairs developed cracks in the tips. I knew that Concepts had a rep for this, and also true to the rumors, Dynastar refused to warranty them. Mind you, they were less then two months old. Regardless of the cracks, I plan on using them another season, before I grab a new twin.
As far as size is concerned, a 180 is the way to go with the Concepts, as the alternate length is actually a 165. If you are throwing big airs, you want the extra length for landings. As far as the Enema goes, the 173 is more like a 175, so it should be fine. It is the better all-mtn. ski, though. Ultimately, I bought the Concepts becasue I found a new pair for $125.
Also, look for a light pair of bindings with minimal lift, to reduce weight and give better snow feel. I have Sallie 912 Ti's on my Concepts and like them just fine. My brother put a pair of Marker 9.1's on his Concepts, and they feel quite heavy.