(Yuu would be the strongest but that's only because he's possessed and basically partially demon because of it, so just keep that in mind, plus there's hellucard but he's more a good guy so hE CAN'T COUNT-)

Mark is one of the strongest. Because since he's a hitman and in case others try to get him he has to put them down, he must learn excessive training, which does make him a lot stronger. (He does have muscles ok-) and he can generally break someone's back in a matter of seconds.

Edd is actually in second, only because he needs to be a butcher and he can't get animals that are already dead. Since his mother killed animals herself, he had to do the same. His speed isn't as high as Eduardo's but he can definitely chase after a animal and cut their head off clean. Which is why he even goes after victims because he could cut their head off.

Eduardo is in third. He's small yes but he was pretty active as a kid. Also the fact he got into fights and had to outrun a lot shit in case he wasn't exactly a match to his component, he does have a very high chance of just being able to run up to someone and knocking them down very quickly. But it's more stamina then strength.

Tom is second because he has to deal with kids. He generally could deal with a kid biting him or kicking him in the shin. Since kids will scream and bite and kick and other shit, Tom has learned to basically be a lot stronger so he can make his kills quick as possible with kids. He makes sure they don't screech too. But say for example, someone got bit by a kid. They'd react badly. But if Tom was, it wouldn't effect him. He's accustomed to actually deal with it.

Ringo may not be that strong but it's very hard to actually hurt him. Since his species there's average weight or underweight, they have great bone strength. Especially for underweight. He could literally rip out a bone and pop your head off like a cork bottle if he could. Since his bones are pretty strong, he can deal with his bones being stabbed or shot at, because he doesn't have too much muscle, but it wouldn't effected him that much. Since his bone is so strong, the bullet would be sticking out and the knife would probably be stuck. Unless it's in the head, then he's fucked

Jon isn't the strongest one but his sides are. Jon, his actual side, is a lot weaker then say Joan or Jack. Jack has some more strength then Jon, only because Jack isn't a full time murderer, since he doesn't want to be suspected and found out as a killer and they end up fucking up Jon. So in his spare time, he legit does do some random push ups or something, just to get himself awoken. So this causes not really Jon but Jack and maybe Joan a lot more strength.

Todd and Tord are the same strength. Tord being the opposite of Todd (sadist, Tord, masochist, Todd) and Todd being the opposite of Tord, it's funny that they have the exact same strength level. Tord is weak like Todd only because he doesn't actually get fit, he's thicker then a fucking thick pipe. Tord often doesn't go for men and more for women, women who aren't like laurel and can literally carry him but women who aren't fit. Basically he kills gender bent versions of himself. While Todd is more a masochist, he doesn't really feel the need to actually be fit. He's a fake therapist, not a real therapist so he can do this. And besides, he gains people's trust anyway, he can chose any victim he wants. So both of them are a lot weaker, but they have different reasons.

By far Matt is the weakest of them all. He wasn't fed and nor he went outside to run around and be fit, nah. None of that. Doesn't even know what the gym is for fucks sake how is he gonna get fit? Since Matt doesn't kill and is just in for the money to make mannequins from corpses (either he found or friends have killed, mostly it's the friends) and then sells them to pay he doesn't need to build it up to chase people like Edd or to be able to put people down like Mark. Though Matt does know some tricks that mark told him, he still isn't strong.

So
That's basically it
Mark is basically the strongest
Matt's the weakest