You aren't going to be happy with either of those subs. Get something that'll work well for your application.
2 hdc3 aluminum coils aren't going to hardly move off of 1200w. You need a minimum of 1500w per sub for these. You will be unhappy with 1200w for a pair of these.
The xfls will need a bigger box than what you'll be able to accommodate and still have trunk space. At a minimum, you'd have to build the enclosure in the trunk and it will COMPLETELY fill up the trunk, and that still may not be enough. Trust me, I've done a 10 cubic foot box in a maxima for a pair of 15s, and it was the entire trunk. I barely had space for the amp. Plus, those subs will want more power than what you have.
Why not get a pair of 12's that will work well off of your 1200w? Or a single 15 that will work well off of 1200w? A pair of sundown sa 12's or a single hdc3 copper coil 15 would be good choices, and there are a ton of others to look at as well.