|suspension first man, it just looks better. A lowered car on OEM wheels look better than a car on aftermarket wheels looking like a 4x4.
^ THIS hands down...
Coil-Overs wont always give it a more harsh ride either.. just depends on settings. Say how low you go vs how soft the suspension itself is.. I personally don't think the ILX comes with a very soft suspension to begin with and it doesn't handle so it's a no brainer in the performance department.. also consider this; if you goto a larger wheel set-up you'll be looking at new tires. I don't think anyone with an ILX is already worn their stockers out yet.
In short: Coil-overs would be the best bang for buck in appearance, ride, performance and cost.