I had a plastic drop in type on my last truck. They do hold up well and they are a bit slide-y, but my additional complaint was that the ribs/corrugations in it were really hard on the knees if you had to crawl in under the truck cap. Overall, did like it.
My current 15 year old truck didn't have one and the bed is um, used enough that there's not much point in adding one now.
That said, I normally haul enough furniture, sand, gravel, firewood, mulch, scrap metal, lumber, hay, and other stuff that's likely to scratch up a truck bed, that if I were ever to get a newish truck, I'd want some kind of protection. I have no firsthand experience with sprayed in liners but lacking that experience, I'm not sure I'd have enough confidence to trust them given the way that I use my truck.