humm... I am sure others will make suggestions at some point but I would be tempted to start with a set of 15mm and try them on the front and rear one side of the car and see what they look like and how clearance is...
if they look ok on the rear but too far out on the front then 15mm rear and 10mm front... else maybe 15mm front, 20mm rear... depends on the ET of the wheels... If they are ET35 (like most reps) then I think they don't stick out as much so you may have to go 20mm rear and 15mm front.
<tuffty/>