[Build Help] More than likely a really dumb question

I want to upgrade my GPU over the holidays. I'm currently running a GTX 560 and was wondering if I can upgrade to any other current graphics card like an AMD 7series or the 660 Ti. Are all slots the same? If i switched from an nVidia to an AMD what would happen to my computer when I started up? My motherboard is a Gigabyte GA-970A-UD3 -- AMD 970. While we're talking about this can you recommend me a good card?