Were I work, usually thunder storms and industrial equipment cause voltage spikes very often on the mains. Making the power supply fail and even burning the devices connected to the power supply.
Of curse you need to put input protection to protect your devices, but since all my equipment has an auxiliary battery. It will be safer to use the battery and wait till the signal is more stable.
In other words I need to check in a safe way, if the quality of the mains AC is good enough for use. I have been thinking that a zero-crossing circuit will help, but industrial equipment are usually AC phased.
Using an op-amp with an ADC seems like a good idea but unless I can ensure they will have no problems with voltage spikes. I will avoid them.