I've been mulling over these exact same quesitons for a long time.
You might check out these guys
www.modularpowerhouse.com in Marietta, Geoergia. They install both systems.
The KB will be the cheaper route of the two, and less invasive. It essentially just replaces your stock setup, with a few changes like boosting your fuel flow, etc. Looks very OE, and will feel a lot like your stock blower (except more so, of course). If you go with the polished set, its a beauty, too.
The HP system is wilder. They swap out your front suspension for coil-overs, tubular K member, tubular A arms, etc. I'd say it would cost almost twice as much as the KB, though it would also give you insane power levels up high on the powerband. You'd give up that mountain of low end torque you're used to, though. Twin turbo rigs have a history of tuning issues, though this would be between you and your installer/dyno operator. Both systems would need complete tunes to work properly of course.
I guess it boils down to where you want to go with it.
The KB is a solid system well-suited to street use and some track action.
The HP is a horsepower monster that will create a good bit of lag time you'll have to adjust to and might well be hard to keep happy in a daily driver.
But if you are shooting for a certain 1/4 mile time slip, the HP is more likely to ultimatley get you quicker.
kenne bell or turbo 
