In order, it'd be: reliability, speed, minimal pain, and mess.
Reliability: Obvious. If I'm gonna CTB, I want it to be done and over with. I've read the posts on here from people whose attempts failed, and they're, more often than not, horrifying in a dehumanizing way. Last thing I need after my failed attempt at leaving this dystopian world is people playing stupid and acting as if wanting out is some sort of unfathomable concept.
Speed: If there's pain, it won't be that bad if the method is fast enough. Besides, as mentioned earlier, I want CTB to be done and over with. You never know if SI is going to kick in, and honestly, it's not worth the risk of allowing it time to develop.
Minimal Pain: Ideal, but with the way this world is structured, it's not guaranteed. However, if I'm going to CTB, I want it to be a painless one.
Mess: Call me selfish or inconsiderate, but I honestly don't care about the mess I make. Why should I? Nobody cares about me, yet I'm expected to care about them? Plus, most people are so desensitized to gore and violence; I doubt someone's CTB is going to faze them. If my corpse does make it on the Internet, it'll probably be on a slideshow with comments like "womp womp" or "blud should've been stronger."