I'm with chas on this.
Time Machine (TM) is the simplest to set up and, after the first copy, backs up hourly and so on, totally in the background. Easy to retrieve individual files or folders; there to provide a complete restore on to a new Mac or new IHD.
Like chas, I have a clone backup drive (in my case using SuperDuper!, but there are others). The great advantage of these is that they create a bootable drive.
You can copy your iPhoto and Aperture databases to a EHD very easily (you can do the same for iTunes & iMovies if you want).
In addition, Aperture has its own backup system which they call a Vault and this is created, again, on a EHD.
The problem with on-line backup systems (and some offer excellent facilities) is that even with ultrafast broadband, it can take forever and a day to upload. If, like me your photos amount to 90GB or more and if, like me in the UK, your broadband is on the slow side - forget it.
I think these replies cover your questions. Need more detail, just ask.
Message for all computer users - Backup is essential and the more there is of it and the more varied in type, the better.
Ian