When selecting a 350cc ATV, prioritize the engine type, typically a 4-stroke, single-cylinder, liquid-cooled engine for better thermal management and longevity. Ensure the transmission system meets your needs, whether it is a CVT (Continuously Variable Transmission) for ease of use or a manual 5-speed for professional utility. Check the suspension system, looking for independent double A-arms with adjustable shocks to ensure stability on rugged terrain. Additionally, verify the braking system, where front and rear hydraulic disc brakes are the industry standard for safety at higher speeds.