We use mainly M4's in the Army. We still have M16's but they are becoming rarer each year.
The Marines still use the M16. They don't want the trade off the M4 gives on long range.
The Air Force still use the M16 as well. I think they just never put forth the logistics needed to exchange the M16 for the M4.
I’m not sure about the Navy, but I can guess the Navy and Marine Corp use the same weaponry.
Right now all 4 use the M9 (Beretta 9mm) as the main pistol option. The M16 and M4 have burst fire options, not full auto like in Vietnam. For full auto we mainly use the M249 saw (Squad Automatic Weapon) that fires 5.56, and the M240 that fires 7.62. Both are belt fed, and full auto only. The 240 has several versions that each has a somewhat different use. They are designated with a letter like the 240B, and 240L. We also have the M2 .50 cal, but it’s not something you normally carry that often.
There are exceptions like SF (I don’t know what they use so don’t ask) but the majority of American forces over here in Afghanistan use the weapons I’ve listed.
P.S. Not trying to sound like I know more than everyone els but I'm setting here with my M4 on my lap in Afghanistan while I type this. So everyone can guess if they want but I see it on a daily basis.