Your highest hit

only counts for 1 hit, not an added number of several hits.

Anyways as far as I've paid attention to my damage, it was 25k with machtbooster and the first offensive skill you get lvl 5 and with a crap non upgraded sword

40k with lvl6 Sonic Boom (retro set 4 effect Sonic Boom lvl+1) with Machtboost
shame it wasnt a crit *W*

btw when enemies are hitted to the ground theyll take less damage-- in case someone has not noticed--

36k with Rena's 1st skill (lvl6) with machtbooster, crit.
53k with Elsword's 1st skill (lvl5) with machtbooster and att buff, enemy on ground, non-crit.
I haven't got any big hitter skills for Aisha...

Oh, and I've found a few tricks.
You can quickly end Elsword's basic fast combo after the 2nd or 3rd hit with a skill, or better yet, a well-timed dash so you can start the combo again.
Any character can make a slightly higher jump by hitting the reverse direction right when starting a dash jump (so push >>^<). I often do this accidentally with Aisha since I prefer regular jump attacks when storming in.

And yes, enemies take 2/3 damage (I think) when in super armor (you can tell by the red lines) when fallen down or getting up.

they dont take reduced damage when theyre using special attacks/heavy attacks and theyre super armored--

oh yeah Rena can quick cast special attacks after using basic attack without finisher
example: melee* Z + Z + Spec attack or ranged* X + X + X + Spec attack

Well, as combat ranger doesn't have good one hitters yet I'd have to say 22k with the first skill maxed.
Though I've done 14X4.6k with spinning kick.

new highest hit with 1st elsword ability, riesen (hugeness) potion and machtbooster pot and with +5 alch made bandit sword 42k
EDIT: non crit