?
I will start us off
1) the straight left hand
2) the right hook
3) the single leg takedown
4) the rear (left) round kick to the liver
5) the rear left round kick to the head
Sometime ago I found interesting statistics of UFC fights since 2012. It was a list of KO strikes. I wrote out just only a southpaw strikes. Now take this with grain of salt because 1) these are only KO strikes; strike can be effective without causing KO, 2)sometimes southpaws fight other southpaws, so it skews the results a little regarding your question how to fight opposite stance, 3)some strikes like left rear leg roundhouse kick can be easily executed by orthodox fighter via switch step 4)I didn't include some elbow and knee strikes since there was no mention from what stance it was thrown, 5)sample size is not that big.
LEFT HAND CROSS 8 KOs
RIGHT HAND HOOK - FRONT HAND 5 KOs
LEFT ROUNDHOUSE KICK - REAR LEG 5 KOs
LEFT OVERHAND CROSS 3 KOs
LEFT ROUNDHOUSE KICK - BODY - REAR LEG 2 KOs
LEFT HAND HOOK - REAR HAND 1 KOs
LEFT FRONT KICK - REAR LEG 1 KOs
CHeck out the source:
UFC Knockouts | MMA Fight DB
As you can see left hand cross combined with overhand cross had 11 KOs in total and left roundhouse kicks 5 KOs with 2KOs from left roundhouse kicks to body made it 7 KOs in total. Then came right hand front hook with 5 KOs. This is pretty much in line with your proposed list and overall statistics from database which place cross in first place, hook second and all kicks in third place.
