GREAT question...
The RC-1 is the
better of the two.
The RC-5 is the
sleeker of the two.
This is coming from first hand experience. When I had a Rebel XT, I purchased an RC-5. It can ONLY do the 2-second delay shot. So, I ended up buying the RC-1 to get the instant shutter option. The RC-1 has a switch to do either instant or 2-second delay shots.
On the other hand, BOTH of these require you to be pointing AT the camera, and in relatively close range, and nothing interfering.
I'd say - Go with a GadgetInfinity wireless shutter release system. I bought this same one (except for a 40D) and it works GREAT. The signal is RF, so you can hold it behind your back while using it and it doesn't have to be pointed directly at the camera. The button on this thing acts pretty much just like the shutter button on your camera. Halfway to AF, and press all the way down to make the shutter click.
Here's a link to the GadgetInfinity ones that work for the Rebel XT/XTi/XSi.
http://cgi.ebay.com/Wireless-Shutte...ryZ64345QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
Now...if you have an XXD series camera, that's a different scenario.