Apples to oranges IMHO.
The Challenger looks cool, is RWD, tons of power but not much room in the back seats.
The Focus ST is a little lighter, more roomy in the rear plus with hatch space, turbo'd and should get better gas mileage- but it is FWD.
So what are you looking to do? Daily driver? Weekend warrior? Any plans on racing it for fun, or modding anything?
FWIW I'd look at the SRT-8 Challenger, bigger motor/more power, and huge Brembo brakes.
1989 Mustang GT: 331, full suspension