I didn't go with coil-overs, due to the cost of 'em. But springs ought to be picked based on the weight of the truck, and whether or not you want a progressive spring. I'm running bronco coils right now, as the front end of the frontier is about as heavy as the front end of a stock bronco, more or less, and I like the flexiness of it. I don't like progressive springs for a rock crawling rig, 'cause I don't like for it to be harder to stuff the axle the farther it gets stuffed; I like the predictability of normal springs.