I went with 17s for two reasons, the first because I knew the 7.5 width would work based on past experience, but the 18s could also work, but 8 inch width may be a problem. Second, weight as the 18 inch wheel usually carries more weight when added to the weight of the tire needed, in other words diminishing returns.
But remember the PCD limits choices in the 17s, so you may not have any 18 inch choice other than GM OEM wheels made for the Cruze.
Those were my reasons, others may have different reasons. Incidentally, the reason I use Discount is sometimes wheels (as well as tires) that look ok when one tries to put them on the car may not be ok.
Laborsmith