When you say "I've always used Nikon cameras", are you talking point and shoots? SLRs? What, exactly? I'm assuming you don't have a library of Nikon lenses, otherwise you wouldn't have asked - so I'm guessing point and shoots. If that's the case, then brand loyalty doesn't really factor in... UNLESS you love (or hate) the camera controls, since sometimes similar layouts are used on a given company's compacts and SLRs.
Try holding these two cameras in your hands, and see what "feels better". Do your friends predominantly own one brand or the other (assuming you've got dSLR-shooting friends)? That could impact your decision because they might be willing to share lenses with you.
Have you shot enough to know what type of photos you like to take? If so, which brand has stronger lens offerings for that type of photography?
I love my Nikon, others love their Canons, either way I expect you'll end up very happy.