Quote from 4wd
I prefer doing offline disc/partition imaging.
What does that mean 'offline'?
The image software either sets itself to do the backup when the primary OS isn't running, (after the next restart), or you physically boot into another OS to do it yourself.
A boot CD/Flash drive, (eg. Paragon's Restoration CD - which will also do backups and a few other things), a separate OS on another drive/partition, etc from where you can run your backup software.
Anything that minimises the chance of the primary OS SNAFU'ing the backup, (maybe because of any programs doing other things at the time).
Why do I prefer it? While it's my primary machine, it's no real hardship for me if the OS bites the dust - I don't use it for anything work related, (because I don't work), it's just a perpetual hobby albeit a pricey one sometimes. A backup image makes it quick/easy but not having one will only slow me down about 3-4 hours - just gives me something to do during the day