Wacom tablets are the ones working best with GIMP since they are the ones with the best Linux support. The two things tend to be correlated.
![Smile :)](./images/smilies/icon_smile.gif)
That said, Wacom is the market leader for a reason, they make very good tablets and the lower-range (Bamboo) is really worth the tiny extra cost in the long run.
Also, wacom has patented a technology that allows them to use pens without any batteries. Most (all?) other tablet brands require a battery in the pen. Maybe not a big deal, but I do find that I have to change the battery pretty often on my Android Tablet (which uses an N-pen with battery).
Tablet-size has little to no importance unless you are a analogue painter used to large, vivid movements. Some claim that small tablets can be stressful to the wrist, I would rather say this depends a lot on how you work personally. I've had both small and bigger tablet sizes and can't say I'm prefering one over the other - the resolution of (wacom) tablets are so extreme it really doesn't matter all that much.
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Griatch