If you're not a Zenith with Retreat Lounge access, I would go with a standard midship IV, i.e. cabins 8255, 8259, 8250, 8254. They're close to the central midship elevators, have beds near the bath and are located in an area of the ship where you have almost non-obstructed views to the water when looking down from your open window.
Concierge isn't worth the upcharge, imo.
Aqua class might be worth the upcharge if you're after better quality sit-down meals and daily spa access. If Aqua, consider midship cabins 9239, 9243, 9236 or 9240.