10" JL Subs for small space. which one?

I have tried reading in past posts and reading a little bit on JL's website, but need a little bit of help.

i have a '02 xstar and was planning on building a box that can fit 2 10's in front of the drivers feet. i have not measured anything yet, but was told that a box could be built for 2 10's behind the existing wall.

which 10's are better for that small of an enclosure? i dont understand the difference between all the #'s.....w3's, w7's, etc.

any help is appreciated.