16 AWG - works for me
The run distance is the key thing to consider. 16 will be fine, especially if it already there, unless you have runs longer than 50 feet. In an ideal state, bare wall, new construction, running 14 AWG or even 12 AWG is a good idea, the wire and connector costs are close and the lower AWG number could be a good investment, same as extra outlets, Cat 6, etc. But, if the 16 is there I don't think you will notice a real world difference, You may, if the type of listening is especially critical, if not I wouldn't worry. I use 16 for my family room HT setup and it works great.
Installing wall connectors is a good thing to do (I had good luck with Leviton Snap Locks) and it allows me to change things around pretty easily when and if I need to