Back in '02 I went through this same dilemma, spray, plastic, nothing, rubber mat . . . There are pro's and con's to each, as everyone above has stated.
I decided on the rubber mat because it would protect the bed and not look like garbage in just a few years. The rubber mat was the cheapest solution with the most impact protection. It could be cleaned to look brand new and kept things from sliding just as good as a sprayed liner.
Spray liners gouge and fade, they become chalky as the sun gets to them. They're fairly expensive.
Plastic liners look and feel cheap and while they do provide impact protection, they are useless against keeping things from sliding around, which for me is a big deal. Then there is the paint chafing thing.
Nothing at all, beat up the bed, don't worry about it, when you're ready to sell it, then either toss in a mat or have it sprayed to make it pretty. Selling the vehicle yourself, you will be able to recoup the cost of a sprayed liner. Trading it in, you will get what you get, the liner won't add any value.