I have a 2006 Ford GT Heritage (with pulley, tune and x pipe exhaust) and a 2000 Viper with Roe Supercharger, tune, Corsa Exhaust and 3.31 gear.
The performance is similar, both incredibly fast, but the GT is actually smoother to drive. Better feeling clutch in GT. More comfortable interior in Viper.
They both get attention but the GT is like a unicorn. I took it the other day to Grocery store and when I came out there was about 15 people around the car and taking photos. Every time I drive it I notice people driving next to me and taking a video.
That being said, there is no better car for the money right now than the GEN 1 and GEN 2 Vipers. At some point soon, these things are going to shoot up big time in value. Look at what is happening to the Supras then think about a limited production, handmade American V10 super car with an insanely beautiful and wild body.