>Is one better than the other

Dyno is far better. It's next to impossible to hear high speed detonation on a rolling dyno. If you only want to pull a few power runs to make a nice chart, rollers are fine but that's about it.

If the engine needs to be mapped from scratch and you really want to make the most of it for a given fuel, i.e. properly map the ignition, fueling and wastegate, then a proper dyno is mandatory. What needs to be factored in is the huge amount of work required to install the engine on the dyno.