FIRST - you want to make an honest comparison, eliminate cartridge. All too many discussions starting with AR vs AK deteriorate into 5.56 vs 7.62x39. If you want an honest discussion (already suspect ) then move forward ignoring it. After all, you can get either one in either cartridge.
SECOND - IIs one more ergonomic than the other? The real point of a gun design is how well the operator can use the controls and accurately fire and reload. As kraigwy said, you can shoot the AR, and drop the mag keeping the firing hand on the grip. What you can also do is load the magazine and drop the bolt to chamber the first round with the other.
The AK won't, you have to move the hand off the grip and cycle the bolt to chamber one. And, shoving the full mag against a closed bolt isn't fun, either. Fully loaded mags have a lot of spring pressure under the top round.
"They're both equally good." is NOT a credible opinion. After all, as said, visit the competitive firing lines of rifle matches and see for yourself. AR's dominate in self loading action competition, AK's fall behind the performance curve. They are less operator friendly, as described. New shooters - and most soldiers are new to shooting - need to have weapons easy to operate. NOT weapons that are harder to load, take longer, and keep the shooters hand off the trigger. That's more downtime to do what a soldier in combat doesn't want to take a long time doing.
If you are combat arms trained, that means professionals determined not only what tactics work best, but also what weapons. Over 65 nations have deliberately and voluntarily chosen to use the Stoner weapons design. AK? Sorry, with warehouses literally filled to the brim, the Russian army generals are actually voicing the opinion that they would prefer something better.
What's better is the FN SCAR, Beretta ARX, Remington ACR, and the M4 - which they ALL copy. The controls, grip, magwell, and use of rails are all common. Look at all the new designs since the M16 - they either enhance it further, or die.
AK's a dying design. Not even Chinese first line issue anymore. Already a Curio and Relic of bygone times, like the Win 94 or 03A3. Nothing wrong with liking them, but they aren't the best in modern combat.