SuperDuper is going to be faster and in my opinion much easier to restore from if you run into trouble. You might also consider Carbon Copy Cloner (which I use). It's similar to SuperDuper and does not require a registration fee. The author does ask for a donation, however. The difference between the two programs is you must register SuperDuper if you wish to use its faster backing up options. CCC is fully functional. Give them both a try and choose which one you like.
I use both to different external hard drives. Main reason is that I am still unconvinced that Time Machine is doing a proper backup of my Entourage identity and my Aperture libraries. You can NEVER have enough back ups!