How to handle VM snapshots to be on the safe side?

Today I had a talk with a colleague about snapshotting Windows machines before updates and I'd like to know how people here handle this.

All of this assumes you have a functioning backup.

You need to install updates and the question is do you create a snapshot while the machine is online and then install updates, reverting to a functioning state if need be or do you shut it down, take an offline snapshot, boot the machine and then install updates?

My colleague said that an offline snapshot is the only good way to do it, but I said that with an offline snapshot I can't be 100% sure that the machine will even start again (Murphy's law and all), but he pointed out that an online snapshot comes with its own set of problems (sessions and writers for example), which is also valid.

What about the double method of an online and then an offline snapshot?

I never really thought about it that much, but how should this be handled?