Sonic: Horrible experience for killers and possibly the worst of them all. Basically impossible to catch up to any of them and if you get hit once you're up to be stunned by all of them all at once, refilling all their dodge meters as they all proceed to peelout and run.

Tails: Not the best experience for killers but manageable. You would most likely avoid open areas while all Tails are camped out in different spots like snipers. It could be a problem if the map favors their flight though.

Knuckles: Probably the best experience but with some issues. A true battle of wits. No healing, no running, just fighting to the death and countering and avoiding each other's hits.

Eggman: The Eggmans would focus on herd strength and group up. They would then all use their shields at once and then run off in groups or scatter.

Metal Sonic: Horrible experience for Killers, and even worse if they all spread out their attacks in a coordinated manner. Fleetway would suffer the most from this. Killing any of them would feel like a chore.

Cream: 50/50 chance that the killer just slaughters all of them due to their inability to fight back, and the way they struggle without springs, or they would be very coordinated and heal up any Creams on low hp which could be a problem for the killer.

Blaze: Basically it would be like dodging spears constantly as if it were a game of Touhou. The spears don't dodge so as long as the killer doesn't get stunned too much, this shouldn't be too much of an issue. Definitely possible.

Silver: Actual hell. If the map favors Silver a lot you are going to struggle to get any of them. Paired with the fact you are going to be dodging non stop projectiles and struggling to catch them flying away or teleporting back, it's going to be a huge mess.

Shadow: The definitive worst. You could be stunned at any moment. There is no moment of safety. Paired with the fact they can fly for a bit and shoot endless projectiles AND their higher than average health and it's just time to throw in the towel. You are going to be paranoid doing this.

If Outcome Memories had survivor stacking (Explanations in comments)