We went with the side dinette for the following reasons:
1) Compared to the front dinette, the big side window helps the relatively small interior space feel much more open. My spouse is somewhat claustrophobic, and she actually likes to sleep on the folded down dinette next to the window.
We actually rented a front-dinette Grandby before deciding and she found it to be way too closed in, with cabinets lining both sides, and the two small windows on each side of the dinette are blocked when you are sitting. So, it was a no-go for us (even though I was initially sure that was the floorplan we would purchase).
2) Compared to the rollover couch, you retain use of the "hallway" and can easily access the stove, sink, refrigerator, etc. without disturbing someone who is sleeping on the dinette area. I am also an early riser, often getting up to photograph the sunrise and morning light. I can get up and make coffee and get out without causing too much of a disturbance.
Note that if you have the main bed pulled all the way out to the "King" position, it will block about 1/2 the dinette table, but there is still room to sit and use the other 1/2 of the table. However, it also blocks much of the sink. Aside from that, the big downside is far less interior storage than either the front dinette or rollover couch.
We have had our Grandby for 5 years and are still happy with the decision to go with the side dinette. It was definitely the best choice for us, but you may have different priorities.
If you can find a way to visit FWC in Woodland or one of the dealers and can tour the different floorplans and visualize how you would use it, it is super helpful.
Good luck!
-Scott