In my experience with older locos, the main generator start system seems to be the most reliable and forgiving. I have dealt with air starts on RDCs and have not been overly impressed. Unless you have another running unit to supply air, or another ready supply, finding air can be an issue but as you stated are easy to jump. Batteries are expensive ($5,000+), but are usually reliable for quite a few years (at least without AESS) if they are kept serviced and properly charged. For shortlines or small oeprations, I really don't see any real advantage to air starts. The air start motors also need regular maintenance and rebuilding, and you still need batteries anyway. The newer microprocessor locos won't even try to start unless there is enough power to keep the computer up while starting.

I did read an article stating that it is expected the AESS type system will soon become standard on automobiles. Can you imagine - every time you stop at a traffic light or for a traffic jam your car shuts itself off? I did drive a modern moving truck a few years ago that did all kinds of wild things - it would shut itself off if you left it parked in idle, would shut down if you tried driving it before it had warmed up (you had to set it to a high idle in neutral with the cruise control for it to warm up without shutting down), and all hell broke loose when I tried to downshift the auto transmission to help control my speed on a downgrade.