Kim,
Taking a short break from packing.
The discussions regarding the optimum focal length of a lens setting for portrait work was geared to the focal length of the lenses of the SLR film cameras. My old Mamiya medium format film camera had a fixed portrait lens which was 80 mm.
When we talk about this in relation to our digital camera we have to make an adjustment. If you will go to this link for your
Canon digital rebel you will see listed a little ways down under lenses: 1.6 x field of view crop (my Nikon multiplier is 1.5). That means that for the sake of this discussion, the 18mm on the low end of your lens becomes a 28.8. And the 55mm at the top end becomes 88mm.
This would be true of all your old lenses as well. My old 200mm lens is now a 300mm lens on my new digital camera! This digital stuff pushes us into a different bit of nomenclature, and it will take a while to catch hold. If the 80mm lens on a film camera was optimum for portraiture, then 53+- is that same number in digital format for your camera.