From what I can tell and based on personal experience the roll on bed liners fail not so much because of the paint itself but because of poor installation practices. That doesn't mean that there is not difference in bed liner coatings. The best diy bed liner material is not easy to identify. I do have some clues as the best paint however.
If you look at scattered spray on bedliner reviews it's pretty clear that the coating material gets the blame for failures. You won't see a Rhino Liner kit or a do it yourself Line-X liner. There is to much chance of a poor job of installation being blamed on the coating material. The big name liners are not going to sacrifice reputation for some paint sales.
You can get good results with most of the liner paints I would guess but there probably is a best bed liner coating. It's not really true that you can get a bed liner in a can. What you get in the can is just the paint. It's high priced paint too no matter who sells it. The key to getting a liner that works is mostly in the installation. It's mostly just in the surface preparation actually.
It takes careful cleaning and some serious sanding and etching to give liner paint a chance to really stick to the bed.
Some of the liner paint makers make it very clear that the prep is where it's at. Those are the ones that I imagine are really providing the best material.
I look at Al's bed liner as a potential best truck bed liner. The Al's paint comes from the same folks who do the Scorpion coatings liners. These are commercially applied and are proven over a relatively long time. The two brands are separate enough that they aren't really linked as brands.
Another plus to the Al's liner is all the options to make the liner much like other liners. For example you can color in to match any color or any look. You can include texture or not. You can make it softer or harder. It's a very versatile finish that can be in it's finished form much like whatever other liner you like.
The best diy bed liner is more dependent on the installation than it is on the particular brand of coating. With that said some coatings seem to really have advantages. The top names may not have the best paint.