I also vote for the spray in, I’ve had the plastic liners and I’ll never go back.
I have used both the line-X and the Armor Thane and I actually prefer the Armor Thane (which is what’s currently on my ram.) I found the Line-x hardened after a couple of years and is very abrasive, it’s why they claim its non slip… but if your stuff slides in the bed it gets scratched up. The Armor Thane is more rubbery and can be sprayed on thicker than line-x and almost feels like a textured rubber mat. I have ¼ inch thick on the bed and 1/8th on the sides. Plus it looks shiny when its clean while the Line-X goes Flat black pretty quick.
It’s entirely up to you, but I highly recommend calling around town and looking at both products before making the investment… After all it’s a permanent mod.
Here are the links to both brands: