I loved both, windjammer (deck 11) for me was easier as I was mostly at the pool (deck 11) and also my stateroom was deck 11. I also loved the food, there was variety and flavour. The main dining room offers an actual dining experience though. I love dining so I also loved the MDR. For me it all depended on mood, I can't prefer one or the other as they have their perks.
Windjammer= tasty, variety, quick, efficient (for me due to stateroom location)
MDR=tasty, service, dining experience
Overall, try both and see what you find easiest and prefer ?