I love adoptables, I truly do, I just don't like when an artists draws a single outline, then poorly colors the same outline hastily with six different designs and throws each one up individually for $10-25 a piece, without much work being put into any of the designs.
I understand it's a quick buck, and so easy to do, but even if you continue to use the same lineart, I wouldn't mind so much if the person actually spent some time with each color scheme and thought out the designs. I know I and several other people would pay extra for a good design or even a customized one, that way it's not just a recolored variant of something everybody else is getting.
When it's done right, I love them.
I also feel that having to draw, write, or win an adoptable is an excellent way to make sure an original design goes to a wanted home, and it gives an opportunity for the new owner to write some new content for the character, but I do feel contests like these should truly be done with original, one-of-a-kind characters and not aforementioned recolored lineart. If you want to be sure someone is actually going to use a design, this is hands down the way to go.