Which machamp move is better?

In your case I will choose KC+SUB (Legacy Moves)
But if you are a hard worker then Look for COunter Close COmbat... IMO... Good Luck!

Counter 11.11 Dynamic Punch 27.41 86.51%
Counter 11.11 Close Combat 35.65 81.88%
Bullet Punch 6.67 Dynamic Punch 27.41 78.10%
Karate Chop 8.75 Cross Chop 27.33 74.71%
Counter 11.11 Heavy Slam 21.90 74.67%
Karate Chop 8.75 Submission 22.27 73.25%
Karate Chop 8.75 Stone Edge 28.70 71.39%
Bullet Punch 6.67 Close Combat 35.65 67.94%
Bullet Punch 6.67 Cross Chop 27.33 63.98%
Bullet Punch 6.67 Submission 22.27 63.75%
Bullet Punch 6.67 Heavy Slam 21.90 62.26%
Bullet Punch 6.67 Stone Edge 28.70 60.29%

you may use the percentage data as attack power reference. Bullet punch/Dynamic punch is far better than karate chop/submission

I am in the same situation. The reason for machamp is, that you want a double-fight STAB-SE-Moveset.
I have my legacy Machamp with KC / Sub at 70% IV and level 30.
My first non-legacy Machamp was a complete fail with double Steel-Moveset.

I use my legacy-Machamp, do not invest in this guy, and i patiently collect its candy (not walk for it, just catch) until somedays i will maybe have a modern pure-fight-moveset.