Depends how you define better. In my experience the APU invariably provides better cooling on board than ground conditioned air. The benefits of APU versus ground electric power depend on how reliable your ground power is. Where I work it's reliability is no better than 50% so it's APU all the time. It's also worth noting that some airfields restrict use of the APU on the ground.
In terms of cost benefits it's very difficult to be prescriptive. Your manuals should tell you the approximate fuel burn per hour for your APU. You then need to weigh that up against what the ground handlers charge you for ground electric/air and how long you need it for. Every situation will be different.