I have the Wacom Intuos Pen & Touch in size medium! It is perfect size for carrying around but not too small. It is around $199 or lower. I love it and it works perfectly. Very nice responding time and pressure sensitivity.
But really, any of the Wacom ones are great. I've had a few, I highly recommend them, and even the cheaper ones are very nice! <3 Good luck with your digital art! It's a fun and challenging adventure
All of the Wacom tablets are good quality. I recommend picking one due to additional features you want - price, surface area, touch input, wireless, number of buttons, and the presence of an LCD screen are some of the most common variations from one tablet to another. All of them come with pen input with sensitive pressure technology.
Chances are they'll feel like the same tablet and you won't detect the difference without extensive experience with various dpi.