What do you mean with 'is it only a family cruise?' The Breakaway does appeal to families, especially those with younger children because of the SpongeBob deal Norwegian has, and so they have activities specifically for younger kids. But it is also a fine cruise for adults with lots of stuff to do, not the least of which is the seemingly endless dining options.
I recently cruised on the Getaway which is essentially identical to the Breakaway other than the theme of the ship. I was on deck 10 and not near any public areas, so I always had to use the elevators or go up or down at least 4 decks to get to a lounge or other activity.
However if you want to be guaranteed to be away from any crowd noise then decks 10 and 11 are preferable. I did note that I could hear noises from adjacent cabins so the soundproofing isn't what it ought to be.
I loved the Getaway and thus I know I'd feel the same about Breakaway. They are very nice ships. In fact I plan to book one of them again for either this fall or next summer.
Just back from our Getaway cruise and we had an M6 mini suite with large balcony on deck 8 forward. I have to say, in my opinion, there is no better location on the ship. You are just steps away from all the activities midship as they are primarily on 6, 7, and 8. We had quick access to the deck 8 Waterfront area from doors right at the end of our hall. Elevators located there as well. And, we found it to be very quiet. I did not hear a peep from neighbors or from the hall once our door closed.
If balconies are important to you, the M6 has a huge one compared to the normal balconies which are little more than "Juliet" balconies. You can even fit lounge chairs out there, but we never asked our steward if we could get one. In truth, we were so busy elsewhere we only sat out there in the early Ams a couple times. Large double sinks and huge shower with 6 jets and rain shower head in the bath.