stage 2 turbo or supercharger for my 03 cavy (auto) and would oi have to do motor mods

Well, both would increase the performance of your car drastically but its a matter of what youre looking for. A supercharger will give its best performance in low to mid rpm ranges, while a turbo would greatly increase the hi rpm performance. The advantage of supercharging is being able to take the person off the line and keep him behind, while turbocharging allows you to either gain on the person, or increase the distance you are already ahead. The disadvantages of a supercharger are that it isnt as powerful at high rpms, it decreases the life of your engine over time, and its more expensive than turbocharging. Disadvantages of turbocharging is the horrible effect at low rpms, and inbetween shifts called "spooling," where theres practically no help from the turbo at all, a lot more complicated to install than a supercharger, and a lot more accessories needed. <blow off valve, wastegate, boost controller, fuel regulator, turbo manifold etc...> Depends on how much u wanna spend, and whats more important to you for your application.