The price difference are probably around $300-$400. I think they both perform well (Spring/Shock combo and Coilovers). It just depends if you want adjustability for the reasons Thinair pointed out.
I'm still debating whether to go coilovers. I really want them to fine-tune the height I want, but I've had coilovers before, and once I've set them to the height I want, that was that, I never touched them again. But, when you up-size your wheels, then you might want to adjust them again. But what puts me off spring/shock combos is that the lowering height is "uneven" front and rear, but there are ways to get around that I guess. I'm lost, but I'm looking into Ground Control coilovers, FK, and Bilstein PSS (last choice because of the spacer issue).