[Joe67]

Having had both for a while...

For a work truck, nothing protects the bed from dings and gouges like a plastic drop in liner. Downside: Looks & over time it will scratch the paint from the bed surface. It will also trap debris and water in there as well. I'd remove it twice a year and clean the bed and replace it.

For a non-work truck, spray in is the only way to go. While it does not protect against dents too much and will tear from things like fork lifts etc, it looks much better than a plastic drop in and is water tight