Most teams who work well together and train also know their team members gear layout and weapons as well as their own.
standardized weapons systems are very simple. Carry M4/M16 Systems so that if you run out of magazines, you can share with a team member. Or the AK47 Variant serious same situation, you can swap magazines easily.
Sidearms are pretty simple specially if you do not utilize them often. Personal preference really applies here.
My Suggestion.
Each team member carries a M4/M16, and at least 6 Magazines. Low/Mid Caps. stay away from High Caps. 1 Side arm personal choice. If you do standardize your sidearm go with at least two magazines.
I suppose it depends on the ops. make up of your unit. Are you a spec ops. unit, urban CQB, or a standard unit for general ops. engagements? MP5s and, of course, the S.O.C.O.M. benchmark M4 series are the most well known for smaller engagements, as is the wonderfully compact SIG 550-552 series, though the FPS are less then the m4/other assault rifles you'll find listed among the AEGs. Also, what are the FPS rules for the events you are attending? If not of a lower FPS rate, try the new M4 SPR MOD (NOD)1. It's around $198.00-$200.00 USD.