Depends on the tempurate where you live,
see this link for some great info:
MOTOR OIL VISCOSITY RATINGS
Viscosity ratings for commonly used motor oils typically range from 0 up to 50. A "W" after the number stands for "Winter" grade oil, and represents the oil's viscosity at zero degrees F.
Low viscosity motor oils that pour easily at low temperatures typically have a "5W" or "10W" rating. There are also 15W and 20W grade motor oils.
Higher viscosity motor oils that are thicker and better suited for high temperature operation typically have an SAE 30, 40 or even 50 grade rating.
These numbers, by the way, are for "single" or "straight" weight oils. Such oils are no longer used in late model automotive engines but may be required for use in some vintage and antique engines. Straight SAE 30 oil is often specified for small air-cooled engines in lawnmowers, garden tractors, portable generators and gas-powered chain saws.
Basically for your car I would run 5W-30, this keeps you covered in warm and cold climates, 10w-30 is the best choice if you live in a climate with temperatures that never go below 0degre''s Farenheight.
Hope this helps