There is the same variety and range of table sizes in all DR's. From 2-tops to 10-tops.
Similar decor, same service level. In the aft section (especially) of the aft DR on Deck 6, you can get vibration and noise from the engines - particularly if the pier departure is occurring while you are are dinner.
As mentioned above, if your cabin is towards the back, you may prefer the Aft DR. If forward, you will likely prefer one of the two mid-ship DR's.
I am not sure of the complete DR operation nowadays, but Princess appears to not be loading up the Deck 5 mid-ships DR's into the MC App for DineMyWay (DMW) purposes. If doing a "walk-up" for dinner, it would make sense to me to head there since guests would not have booked there pre-cruise. I am not sure if that DR gets added to DMW once the cruise begins and it might be the best choice for a daily reservation.
PS to Others: (I would like to know if the 3rd DR ever does show up in DMW for booking).