Which Machop to evolve?

If you're hurting for Machamps, just evolve them both and bring'em both up a few levels. Will be fine.

All things equal, your L33/5A Machamp does the same damage as a L28/14A will. Do you have enough TMs to adjust your newly evolved Machamp(s)? When I faced the same decision that you are making, I opted not to evolve Machop because I have a good Hariyama, and dealt some good damage yesterday with 5 Machamp and 1 Hariyama.

Both are mediocre. Do more Machamp solos or use your Groudon instead.

Both are decent enough. if you're facing dracometer you can get through 10 or more even in a reasonable sized group. Don't forget you'll often need 3-5 charged TMs per Machamp to get dynamic punch.

I would pick one of the two machop and have an even 6 DP Machamp, then a B squad with a few hariyama. Most times you need help from the B and DP hariyama is also very good.

https://pokemongo.gamepress.gg/breakpoint-calculator#/

Use the breakpoint calculator to help compare the IVs. With 15a and best friends, the last breakpoint for Counter is reached by level 31. Making sure that most of your Machamp can reach that breakpoint will be a lot of help.