Well I highly recommend Wacom, I use the Intuos5, A3 at present - it allows you to use both your hands as well as the pen, and once you get used to it you will very quickly speed your workflow up immensely. An A5 sized version might be a little difficult to use as they scale sharply on a large monitor... the slightest movement on your part results in the cursor flying across the screen at up to 6x the distance.
I can also advice against hunting for a cheap make on ebay. I did that before investing in the Intuos5 and although these cheaper tablets claim to have similar tech specs, i.e. same number of pressure levels etc. the difference between them is overwhelming. My cheap tablet broke after just 8 months... If you're going to be using it every day, this is something worth investing in.