You have 5 great vehicles to choose from and any choice you ultimately make, you will be guaranteed to get a great car. The 2010 Ford Mustang Shelby GT500 would probably be the better choice. It is the fastest, has the most lateral grip and they hold their value quite well. The 2010 Ford Mustang Shelby GT500 has been said to be the best looking one yet and offers more than one might think. The GT500 will hit 60 in just 4.3 second and will pull 0.92 G of grip. The Camaro SS and Infiniti G37 will only pull 0.88. The Mustang GT500 has the classic supercharger whine when under VCM II harsh acceleration and has been to said most fun-to-drive when it was compared to the vehicles you listed. In a 2009 Car And Driver comparison the Mustang Shelby GT500 beat out the Chevrolet Camaro, Chevrolet Corvette ZR-1, and Nissan 370z Nismo. You may ask why would it matter if it beat the ZR-1 and Nismo? It matters because if is beat the top of the line models of the cars you want to buy, could you imagine the base models compared to the GT500. The only thing that could be better for the GT500 are the brakes. They are not bad, they could just be better. If you go with the 2010 Ford Mustang Shelby GT500, you would not look back and ask "What if?" The other cars are not bad cars, the just cannot meet the GT500 in terms of power and fun-to-drive factor.