Wow, I don't know how I missed this post before. I gotta stay on top of this forum more. LOL
Another hat for the Twin-Screw ring - Saleen. I chose it for several reasons: Quietest whine (I like to sneak up on my victims, though the exhaust kinda messed that up), and stock-looking appearance. It looks like it BELONGS there. Black, wrinkle finish, long intake runners, pulley below the throttle body (so you can't see it unless you look under the inlet tube), and the TB is in the front, in the center, almost in the stock location (it's just raised a little).
If you do not plan on EVER wanting to make more than 16 PSI, then Saleen might be a good choice. Brenspeed and JDM both do EXCELLENT work (Brenspeed did mine, ultra-safe tune and a/f on the dyno). The base kit makes like 4.5 pounds which will get you to around 380-390 wheels. I added a smaller pulley, injectors, a CAI, and a custom dyno tune to get where I am. I'm still running the stock bottom end, but I don't beat the car on a regular basis (once a week or so I'll get on it on the highway).
No matter WHICH blower you decide, you'll need a new clutch. Trust me. After having the Saleen on for one season, my clutch is SHOT. Car has 25k on the clock.
Between Whipple and KB, my vote is Whipple. The cases are aluminum, so they bleed heat better than KBs. A local guy here has a KB, and it's just one giant heat sink. One more shot at KB - Saleen cars are OEM and are sold with a warranty. Whipple makes the blowers for Ford's kits. KB? Aftermarket only, no drivetrain warranty..
Speaking of warranty, if you get a Ford-branded Whipple kit, and have it installed at a dealership, you can keep your drivetrain warranty (or a portion thereof). You can also get a 12,000 mile warranty (I think - or maybe it's the balance of OE?) if you have the STOCK Saleen blower installed by Brenspeed or JDM. There is also a Saleen Extreme blower which will keep your warranty and get you 475 crank HP. The stock Saleen kit is rated for 435 crank, IIRC.
Roush?

It's a roots. Yuck. Loud, hot, and ugly.
Either way, unless you're planning to go all out and do the bottom end and make it a track-only car, any of the kits mentioned will provide more than enough power to have enough fun on the street to land you in the clink.