Room Acoustics and Speaker Placement

I am not a guru, but although I’d think experiment with both if you have the outlets available (or enough speaker cable) I’d THINK having the sidewalls but having whatever is in the dining area as a rear wall would be the better option.

I’d THINK that with this option, your reflection points to  the side would be equal, and if they were not, I would also THINK that your left/right balance would be skewed.  As far as the dining room where the back wall would be, at least there will be stuff back there for diffraction and I would also THINK it might be advantageous to have that as opposed to a reflection off of a back wall that was closer.

Neither is ideal. But if those are the only choices I'd go with option #2.

 @ozzy62 & @immatthewj Thanks guys!

With option 2, the side wall on the left will be farther away as compared to the side wall on the right.  Is there anything I can do to minimize the skew? Would toeing in help?

The distance to the sidewalls is important. If they are far enough away, then the asymmetry doesn't matter. 

As long as you don't hear a shift in the center image you should be fine. Hopefully the one that's closer to the side wall isn't very close.