Guys, I'm going to get a larger set of wheels, but what offset should it be? I want it flush with the wheel arch. any idea?

these are the one I'm planning to get, haven't decided on the size yet, 17 or 18

http://www.work-wheels.com.hk/produc...?product_id=68
or these
http://www.work-wheels.com.hk/produc...?product_id=69