If I had to pick a problem with physical attacks, it would have to be how easy it is to perform a kick over a punch. Yes, I know if you miss a kick you can fall, but the amount of damage done with a single kick is pretty significant. I know the punch has a 1 in 6 chance of hitting the head, but the kick has a much better payoff because you can consistently hit a leg location. You can flank a target from the right or left to pick a leg.
Remember that you get 2 punches, but only one kick. The -1 ease of attacking is offset by the risk of falling if you miss. Yes, you can pick a leg, but it takes a lot more damage to take off a leg than to breach the head armor. The punch still allows you to target back locations from behind the target, particularly after you've created holes in the weapons phase, where the kicker still has to go after a leg. I find kicks MARGINALLY more effective than punches, but if the to-hit modifiers were the same, I'd lean toward punching in most situations.
I generally prefer low piloting skills over low gunnery on some lighter 'Mechs, because their actual firepower is limited, but they can kick to inflict piloting rolls as well as do some damage. I recall taking out one Atlas with pilot injuries almost entirely from failed "seat belt checks" (with the aid of a 2 point MG hit to the head) inflicted by a Locust while the Atlas was preoccupied with shooting at more threatening targets. Once the tonnage of the attacker gets higher, the effectiveness of punches to the head starts to take precedence.
Probably the most effective physical attack I ever landed, back in the dim and distant past, was a push: knocking a lightly damaged Assault 'Mech off a 2 level cliff into water. Granted, the fall damage wasn't spectacular, but the head failed its breach test. One drowned pilot. Unfortunately, the simultaneous return kick ripped the leg and torso side off my poor Light 'Mech (It was either a Wasp or a Stinger) that dared to push the Assault. I'll gladly make that trade again.
Then again, I've been in one game where a Clan assault failed its piloting roll to cross a small stream, fell face first, and breached the cockpit on the opening round of the game before anything was even in firing range. Physical attacks, falls, or other non-weapon damage can play a big part in a game, and I often consider how to best utilize the terrain to exploit that (such as high cliffs, water, etc.), rather than heading for a nice patch of woods or partial cover to trade fire in a session of TurretTech(r).