you can't do a list like this without setting the rules before hand. You have to say things like, prep time, location, is the character suddenly willing to kill, airspeed velocity of laden swallow, etc. I'l ltryu and take this as cereal as possible.
Flash Tier:
Flash - Tier of his own, depends on which version of speed force bullshit applies. In some he simply cannot be touched, and he could infinite mass punch and infinite number of opponent an infinite number of times before they were even born. In others, he's just fast, but can't even outrun explosions or through well planned strikes.
S Tier:
MMH - If he cut loose, nobody could even touch him, could lobotomize, cripple or even kill a person with a thought, but vulnerable to fire even when "phased" so not Flash tier.
Wonder Woman - Powers that rival / exceed supes, +trained to kill, +willing to kill.
Supes - Stronger than Doomsday, has exploitable weaknesses, tires.
Zod - Previously lost to Superman, relies on weaponry / help that may not be available.
Doomsday - Practically invulnerable, does not tire, but tactically inferior to others. Previously lost to Superman.
Lobo - Czarian's more killable than Doomsday, but not by much. Probably sloppiest of the heavy hitters, has lost to Superman and been outwitted by ordinary humans.
A Tier:
Adam - Killable / Depowerable, but willing to kill and probably has better understanding of powers than Billy (1000+ years of experience, even if most of it was in space).
Shazam - Possibly even with Adam, but he's got a conscience (And the mind of a kid/teenager, depending on the writing)
GL - Only as strong as his will, which would presumably deplete if he tired. Has lost to everyone above.
Sinestro - Same as GL, Hal has been documented to have the greatest will of all the Lanterns tho.
Zatanna - Could be as high as Flash with prep, as high as WW via sneak attack, definitely tops Adam with free reign to speak, but down here in any impromptu engagement against a character fast enough / capable of silencing her.
Aquman - Exceptionally strong but requires help he probably would not have, can neither fly or survive in outer space.
B Tier:
Deathstroke - Goes even with Batman in impromptu contests, seems better at "quick" planning, could probably actually take Killer Frost, Raven and Cyborg because he is also willing (and usually intending) to kill.
Raven - Exceptional abilities, but not as good as anyone above without help / prep, has lost to Deathstroke.
Cyborg - Super strength + intellect + arsenal of ranged weaponry.
Killer Frost - Immediately defeats anyone who relies solely on physical combat.
Batman - Could be as high as flash with prep, otherwise "limited" to exceptional physical combat prowess and willingness not to kill.
Green Arrow - Ranged game makes him more of a threat that anyone below, but lacks batman's tactics and can't take anyone above without the right quiver (prep).
Lex (In a suit) - Could go higher with prep on gear alone, otherwise lacks tactics and physical prowess of everyone above.
Hawk Girl - Should be higher, but has been defeated /outsmarted by everyone above her.
Bane - Cyborg without any range, requires venom, defeated by Batman.
C Tier:
Grundy - Identical to Doomsday, but vulnerable to a ton of stuff everyone above could and probably would have on them.
Joker - Has beaten everyone below, completely unpredictable.
Batgirl - Trained to fight by Batman, better arsenal / smarter than anyone below
Nightwing - Trained to fight by Batman
Catwoman - Actually probably dead even with the wing, but he's a lady killer so she might succumb to that.
Harley - No combat training, no powers, no prep. Vulnerable to Nightwing's charm.