I've cruised solo (and not solo), and also been to AIs. I think that as a solo, you'll find a cruise much more conducive to meeting people, especially on Epic. In general, the entertainment will also be a step up on a cruise. The one place an AI might win is that they generally have an activities staff who'll encourage you to get involved in sports/activities during the day, where on a cruise you'll drive your participation. But I'd say a cruise wins, hands down. (Though do be prepared for a higher spend on a cruise, since it is less inclusive than the AI.)