Not sure if this is the right place but we have been having ongoing discussions on how to best drive spikes, doing it manually is getting old, as are the spike drivers.
Electric, would be cheapest but would be 120v and need a generator and I am not sure about the efficacy.
Air, would need a Compressor and probably a tow behind, but a compressor would be useful for other things, because of the altitude compressors get significantly down rated.
Hydraulic, that is how BNSF do it, we would need a PTO but that seems available and the hoses.
On the basis that benefiting from others experiences is usually the best way to go wondered what others found going through the process. Now if a Hydraulic comes available free/cheap whatever I am sure we will grab it, and a lot depends what we can get for not very much.