If you're talking transatlantic, I recommend the ship for a single traveler.
I went with a friend, but there were singles activies and the pace of six nights at sea lends itself to meeting people. Everyone hangs out in the library and bars, it's laid back and casual. I would take this ship as a single in a heartbeat.
I suggest requesting a large table and asking them to put you with other singles.
It's dressy at night, three nights are formal. But this ship certainly deserves it! In the Queen's Room with a 16 piece orchestra, people in gowns and tuxes ball-room dancing. It's like stepping into a movie set!