What size Wacom Intuos tablet should I get for drawing?

I'm a high school student, looking for a starter tablet since drawing is just a hobby for me currently. I've looked at multiple forums and discussions already but can't find the information I'm looking for. My question is which tablet size should I get: small or medium. I was going to get the small but then I saw some articles saying not too. My computer that I will probably be using is 17inches across, and almost 20inches diagonal. My hands are average to small size, and I'm used to drawing on A4 paper, but my drawings rarely take up more than 2/4th of the page. Any help would be great! Thank you :)