Which is worse?

It isn't a fair comparison or question because the roles aren't equal. A scumbag Killer (however you define that) is just doing his/her job regardless. Nobody relies on them because they aren't part of a team (at least until we see 2v8). So good manners or bad manners, a Killer that is playing within the rules is still is functional and carries his/her weight. Even when the Killer DCs the Survivors don't suffer (pretty much only the Killer does).

An Entitled Survivor has a team he/she can let down with bad behavior. The Role is responsible to other people and every hissy fit, disconnect, and so on impacts other people playing the game deeply. Entitled Survivors also go outside the game and attempt (far more often) to create unofficial rules, moral and morays they expect others to play by despite them having no basis in the rules. They are far more detrimental.

All that being said, in the real world a bad sport and jerk is still a bad sport and jerk and I wouldn't want to hang out with either. In the game, however, there is no competition as to which is a problem.

I based this on the following assumptions:

"Entitled Survivor" is a survivor who will use endgame chat or send a message complaining about a perk being used, not being allowed to escape or some petty complaint that really doesn't need to be dealt with. All the while, they happily BM'd throughout the trial.

"Scumbag Killer" is someone who deliberately tries to make the trial miserable by humping a fallen survivor or decides to just cause a bleedout.

The difference is in the endgame. A "Scumbag Killer" in my opinion will just wait for comments to come in, whilst an "Entitled Survivor" needs you to know how annoyed they are.

Both are tossers, but being entitled is worse than being a scumbag. By that reasoning, were the question asking whether an "Entitled Killer" or "Scumbag Survivor" was worse, I'd say the "Entitled Killer" is worse.