The RC-1 allows instant picture taking, 2 second delay picture taking or bulb exposure (open signal and close signal)
The RC-5 only has a single mode with a 2-second delay, but the advantage is that it is very thing and light. I use one of these whenever I have to be in the shot itself, because it gives time to hide the remote before the actual shot.
There is also the RC-6 which will operate in either 2-second delay mode or will instantly take a shot (like the Canon RC-1 Wireless Remote).
My recommendation would be to get the RC-6 which is conveniet, cheap and small enough to put on a keychain or on your zipper of the camera bag