They can also be chambered for the 6.8 Winchester SPC.Glocks, because I love them.
And I would go with an ACR because they have such an effective anti-recoil system and you can change the calibre from 7.62 to 5.56.
I'd have to go with an H&K G36, and an M1911.
Let's be honest, as much as I love the .308, and .338, the better choice for assault, and riflemen would be the 5.56. It's very accurate, and an 8-month old can handle that recoil. I chose the G36 because, well... H&K. It's so much more practical than an M4/M16, or other AR variants. The ambidextrous bolt handle, and selector make it very convenient for any one to use.(The M4's design is retarded. you have to take your hand off the trigger to load it.) The G36, is also much more reliable, and has over 1.5x the effective range of an M4. Maybe I'm just a G36 Fanboi. Not that I don't like AR's I love them. but they're not as practical.