I for one absolutely HATE drop-in plastic bedliners. They warp, crud gets under there and promotes rust even faster, and anything that can slide on it will.....a lot. Annoying.
Definitely talking spray-in, roll-in, paint-in etc. here. Now, mine came with the sweet factory rubber mat, which I will probably put back in, if for any reason because it says Jeep on it. But it has the raised, hard "feet" all over the bottom of it that keeps it from just laying pressed against the metal, so it has done a great job because when you pull mine up the floor is perfect. But, my PO also ran a cap on there most of the time too. ;)