If you are in the business of running a warehouse or own a rental fleet and are directly comparing new AC vs DC, then AC would be the choice. As others have said, less parts, less maintenance, etc.
With a fleet of trucks my experience is the TCO will be lower on AC. With 1-2-3 pieces the cost savings will be minimal, especially if an AC controller needs replaced.
Choice of equipment manufacturer will have a big impact on whether there is any benefit to an AC powered forklift. I have many Crown Reach Trucks/ SP's I service and the costs are all low. My rental fleet is mostly Raymond Reaches/ OPC's, the costs with the AC is much lower. The new AC units are much better than a DC Easi that was expensive to run.
Do not do much work in high cycle environments like grocery so I have not seen the benefit of faster speeds. My current belief is that the productivity is close enough to be considered equal.

If you are moving from an older Raymond Easi to a new AC