Nothing! And in reality, you shouldn't listen to what anyone says when it comes to keyboards or a mouse. These are extensions of YOUR hands and therefore they must feel good to YOU - not me or not Joe Blow. You need to go down to your local electronics store and play touchy feeling for yourself and then decide what feels good to you. Also take note of where you will place this keyboard. If your desk has a keyboard tray, is it wide enough to hold the keyboard and allow for adequate mouse movement? Some keyboards have special buttons on the side making the keyboard 20 inches or more wide. Some keyboards have special buttons above the keys so the keyboards are deep - maybe too deep for you. Only you can decide for that. Some folks like a soft touch key, some like solid. Some a short throw, some long. Some want silence, some a solid click. Again, you have to decide.
The only advice I can really give is to get a major brand. I don't know who makes Microsoft keyboards and mice, but I know they are excellent. And Logitech is well known for quality boards. And Razer is getting notice for their game boards. Also note that money talks. If you want quality, stay away from budget boards.