I have used the W6 and the W7.
I have built ported and sealed boxes for both.
In the end, I am using a single sealed 13W7 on a 1200/1. The 13W7 uses everything the 1200/1 can deliver. 2 of these sub's on a single amp would be woefully underpowered.
It gets low with authority and has very sharp, hard hitting response. In the cab of my truck the 13W7 can make passengers feel like the air has been sucked out of their lungs. The W6 could not do that in my setup.
For me, ported on both subs was slighty louder, but I lost the accuracy and low end authority that I enjoy when running sealed.
I have used the W7 in an oversized sealed enclosure and in the JL spec enclosure, and I personally don't think The difference is worth losing the additional volume in the vehicle.
I also felt that the W6 handled above 50hz marginally better than the W7, but at a loss of volume and sub-30hz hit.
The W6 is smaller, uses less space, and can use a smaller amp, so it gives you more options.
Ultimately, I think the W7 is right for me. Audition both if you can though, because the mild differences might matter to your tastes.