svt for pure muscle and roush for awesome looks and lots of speed. If i had the money it would be a roush though.
Performance wise, most people already have a saleen or roush, and some look it too. IMO SVT all the way. DOHC is kick ass, the heads flow ALOT better = more power, and I like the idea of an IRS. I know the solid rear is good for drag racing, but I want a better ride on the street. I hate feeling the rear shift around over bumps. I would love to have a 00 Cobra R myself. Looks awesome, and a 5.4 DOHC with the best flowing modular heads sounds damn good to me. Wouldnt mind owning a terminator cobra though...very sweet.
SVT, as far as bang for the buck performance is concerned. As far as looks are concerned, Saleen and Roush will turn more heads. But I'm the kind of person who shoots for performance then looks.