If you want the best power/torque to price ratio, this is the car for you. You get more than double the torque and power of many so-called sports cars, and for less than double the price. The ZL1 has better ride quality (like the CTS-V) than the GT500 and would have a more comfortable ride for daily use. However, the ZL1 has lousy interior ergonomics, less comfortable seats (IMO), and outward visibility is lousy for daily use. The CTS-V is a better choice than the ZL1, unless exterior styling or price are major factors. The GT500 weighs about 300 lbs less than the ZL1 and has an extra 80 hp, giving it a substantially better power to weight ratio. I've also heard many ZL1 owners complain about the launch control system, and though the system in the GT500 has faults, it's better than the ZL1s. (The GT500 lets you choose the launch RPM, and the ZL1 decides for you based on temperature, barometric pressure, and a host of other variables).
In the hands of a capable driver, the GT500s handling isn't far off the ZL1s. I will say that based on my experience behind the wheel of the Shelby and CTS-V, the CTS-V (or ZL1) is easier to drive fast for someone unfamiliar (like myself) with either car. Some critics have even argued that the GT500 is better balanced, but I can't agree with that. I test drove three different CTS-Vs (one manual and two automatics) and the magneto suspension is very comfortable in the normal touring mode and it firms up and inspires confidence in the sport setting. Despite the comfort, they did feel heavy and didn't have the same fun, sporty feel as the Shelby. I test drove three different Mustangs including a 2012 Shelby, 2012 Boss 302, and 2013 Roush RS3. Nobody would allow test drives of the '13 GT500. The Shelby or the Boss would make a great daily driver, but the Roush wouldn't, at least not in my opinion. To my surprise, the Shelby and Boss felt very refined and were very well rounded cars.
Don't let us decide for you. Go out and see for yourself. Take a Shelby, ZL1, and CTS-V for a test drive. If you can't find a '13, test out a '12 model. Everyone likes different things and what's important to one person may not be important to someone else. I also recommend you go to some other forums for information direct from current owners of all the cars you are interested in testing/buying.
2013 Shelby GT500 - New!
Capitol Raceway, Crofton, MD: 11.90 @ 127.14
2008 300C SRT8 (Inferno Red) - Sold
DiabloSport Predator (93 Octane Tune), Jet 180* t-stat (JET-10183)
Toyo Proxes 4 --245/45 Front, 275/40 Rear
Option Groups 1 & 2, Power Sunroof, 13 Kicker SRT Speakers
Capitol Raceway, Crofton, MD: 12.861 @ 111.53 mph
75-80 Dragway, Monrovia, MD: 12.905 @ 109 mph