Spoilers are used to create downforce on the rear on the vehicle. But forgetting the idea of spoilers, think about what look you like best. Do you like a big chunky spoiler, a small subtle one, or no spoiler at all?
Make your decision.
Spoilers do what their name suggests. They 'spoil' the air flow. By doing so, they reduce any lift generated by low air pressure flowing over the back of the car (ignoring front spoilers here). The don't actually create downforce. For downforce a properly designed wing is required. This has an aerofoil cross-section but, instead of creating lift as when used on a plane, it is inverted and so creates 'negative lift' or downforce. The problem with this is drag is also produced, so they will help in bends (properly designed wings, not the sort sold in go faster mags) but slow you down on the straights (especially the sort sold in go faster mags!).
The sort of 'spoilers' sold to car modifiers, although looking a little like wings, are so badly designed that they will act as a spoiler; breaking up the airflow so possibly reducing lift (if there is actually a low pressure area to deal with at the spolier's position) but will greatly increase drag. Look at the Skylines running at the TOTB meets. For the top speed runs they remove their huge 'spoilers'.
Being of the very old school, I adhere to the philosophy of only fit it if it has a use, then deal with making it look right. Of course, this 'use' could be purely for cosmetic effect, but don't then expect, or claim, performance improvements.
Now, what was the question? Oh, yes, what do I prefer? Fit for Purpose. Subtle.
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