Now Box mags are a whole different ball of wax so we will leave those out. Also we are gonna leave self winding mags out since they are way up there in price and are not commonly seen.
And I will give the rattle factor to the high caps and the realism to the real cappers... but the rest does not add up.
I'm going to use my gun as a base line so things stay fair....
I have a G36k where the base Hi cap mag is 470 rounds and the base Mid cap mag is 100 to 140 rounds. We will use the 100 round for my explanation.
So the biggest 2 arguments I have heard against Hi Caps is:
#1 People who have them just spray and pray
#2 It isn't realistic
So let's kill #2 with a shot thru the head right away. The standard amount of rounds in a battle rifle today is 30 so right there that throw the whole realism thing right out the window. So taking a standard load out as far as I have been able to find of a Marine is 8 mags plus we will give him one in the gun and one piggy backed to that (10 total). So at 30 rounds each that is 300 rounds, way less than the same # of mid caps for airsoft which gives the player 1000. Not very realistic no matter how you look at it ...
Now let's look at #1 and kill it easily too. People say that if you have Hi caps you just spray and pray where I find that to be quite the opposite. Mid caps do not have to be wound so you can unload all 100 rounds with one pull of the trigger if you want. With a hi cap after about 30 rounds you have to wind it back up or you are just shooting little balls of air that have no effect on anyone. (which going back to the realism thing actually simulates a mag running out better than 100 shots down field then having to reload)
It takes me roughly about 2 to 3 seconds to fully wind a hi cap mag back up (at which time I'm behind cover) and roughly the same amount of time to drop a mag and grab one from a vest and slam it home. If I have the mags piggybacked it is even quicker because I can just shift over to the next mag in less than a second. So in that light a Hi cap actually takes longer to unload 100 rounds than it does from a mid cap.
Let's look at the # shooting 15 RPS for 100 rounds
Hi Cap - 30 rounds 2 second wind 30 rounds 2 second wind 30 rounds 2 second wind 10 rounds = 12.75 seconds
Mid Cap - 100 rounds one pull of the trigger 6.7 seconds
So with those numbers I can safely say that you can spray and pray easier with mid caps than you can with Hi caps. So even adding the reload time in for the mid caps you will still be able to send 450+ rounds down field with a mid cap much quicker than you can with a hi cap.
Now let's look at some of the players I have seen on our own fields that are fully loaded with 3 double mag pouches per side of the vest and 2 attached to the gun. That is a total of 14 mid caps or 1400 rounds of ammo compared to my 1410 I'm carrying in 3 high caps. Now this is also the guy I see most often in respawn/behind a tree either reloading all his mags or at least a good portion of them.
So saying that you are more conservative than that and you only carry 8 mid caps and in a 4 hour game you use up roughly 3/4 of those that is roughly 600-650 rounds you sent down field. In an average 4 hour game I have yet to go thru more than 1.5 of my hi caps so I have sent only about 705 rounds down field not even taking into account the 30 or so that are still in the empty mag because the hi cap does not push them all thru. So deducting that 30 rounds guess what we are almost equal in the # of rounds... Hmmmmm go figure.
So the whole Hi cappers are just spray and play players doesn't hold water either...
Now it is up to you to choose which you will use but I personally prefer Hi caps because with the G36 Mag I can have 3 comfortably attached together and loaded on the gun. This means I'm not weighted down by a vest or a bunch of metal boxes holding roughly the same # of rounds attached to my body. It means I can move quicker and easier and for a fat old dude that is a real plus.
This whole debate is just another Ford VS Obama Motors thing and really just depends more on what you like to do than if there is a real difference.