Which is safer, a general anesthesia, or one from the spine?

Essentially the same. The risks of serious outcomes, that means death, are essentially the same. Some procedures need a general anesthetic, while other require a regional or spinal one. Each has their specific risks, but overall the risk is the same.
Safest. The safest is the one chosen by you and your anesthesia provider based upon your procedure, your history and your anesthesia provider's expertise.
Both. In general spinal anesthetics carry lower risks of complications. These in general would be infection (which would be serious), and under special circumstance paralysis from bleeding. These are rare complication. Headache would be the most common. The complications from general are more numerous however and carry a mortality of about 1.1 per million.