There are two humps on Oasis. The aft one has no rescue craft (that's what they call the lifeboats on Oasis) below it, but really, the boats are tucked in under an awning so it doesn't matter. Personally I would go with deck 6 because it is closer to the promenade, dining room, Boardwalk, which are just a set of stairs away. No waiting for elevators.
A word about balconies...while I normally get a cabin with one I really don't use it that much, and I venture to say this is true for most cruisers who may spend an hour a day on it on average. There is so much to do on this ship that I wouldn't want to waste too much time sitting on a balcony. Just my opinion.