I'm looking for a camera that might replace my current camera. I'm thinking on this 3 models. Well, I can't seem to see the differences between the Cannon SD500 and SD500 (both seem to be 7.1 Mpixels), is there any difference between both models?

And also I've seen the Nikon P4 and it also looks pretty nice.

What would be my best choise?

I've heard a lot of stuff about the cannon, that the processor it has is very good, and I think that the SD500 has a newer version. I don't know if that's the same for the SD550, which I would think so. I have a A520, and I like it, so the idea of a newer Cannon sounds great. One thing I like on the A520 is that I can set a 1 second delay, so I can press the shutter button, and then just hold the camera to be it steady.

On the Nikon P4, I was able to try it at the store, and it seems to be fast responding, and it has a vibration reduction feature, which I think it would help for my not-so-steady fingers. If this works to reduce camera movement, I think it would help when someone other than myself takes the picture.

What I want the camera for is not the resolution, but I just want a camera that is fast to turn on, and to take pics. Also pic quality is a concern. I do mountain biking, so I want a small, portable camera, and if the case is of metal rather than plastic is a big plus.

1.I think that both cameras are aluminium, so no advantages here.
2.On the resolution, the Nikon has a little higher (8 vs 7), but I don't think it's a dealbraker. Unless, that is, everything is the same.
3.The cannon has their newer image processor, which seems nice, and I think that I've heard from several sources that the Cannon image procesor set their cameras above the rest. I don't know how they would compare versus the one in the Nikon.
4.Speed. What I mean is, not that they can compare vs a SLR or a profesional camera (I don't know if that's the right term) where you can take like 100 photos in a second, but that I can take out of the carring case, turn on, and snap a pic. Also, taking another after taking the first.
5.How often does the camera find an image where it freezes trying to find the right settings (my other camera is a HP and about 10% of the time I get a 'Processing' image and freezes up).
6.Can you save your favorite settings so you don't have to set them each time? The HP has a 'MyMode', which saves all the settings, so that once you set up a setting, you can just turn on the camera and that's it.
7.I 'think' that on the Nikon you only can adjust the resolution from best, better, med and low, and on the Cannon you can choose the resolution, and the quality of compression separate. Am I right here?
8. The Nikon has the Vibration Reduction, so I don't know if they're comparable, but I think that maybe 10% of my photos comes up blurry, so if the VR thing helps for this, maybe this feature can be usefull. But I don't know if the VR is more a marketing stuff.

I think that sometimes comparing two brands is not a black and white decision, one brand will have better something, while the other would be stronger in another.

Any help you can post here I would appreciate it very much!

Thanks