putting on an after market exhaust will require a tune to remove the mil/check engine light, caused by incorrect readings on the 2nd o2 sensor. you can drive without getting it tuned, but the o2 sensor tells your cars ecu how much air and petrol to inject into the motor so you can run to rich or lean without it. having a tune will also void your warranty. as for best exhaust, depends on your own taste, i currently have wildcat extractors, no name hi flow cat, and twin 2.5 stainless steel going to quad tips by hm headers on my g6e. i like the sound and its non-droney. redback, lukey, and manta also have good reputations
