I think the edge would be the best choice. You have both - the opportunities of an eInk-Device and the features of a tablet. I don't own one myself (I own a tablet PC and an eInk Device). But to have both options in one device is the best thing if you need it for studying. I don't know an eInk-device that is good for anything else than reading.
If you want to know if the edge fits your needs watch all the youtube-videos out there. It is not the perfect device (e.g. no landscape-mode on the eInk-Display) but if you don't want to walk around with two devices (which, in my eyes, is the best idea) you end up with this device.
The only alternative would be devices with a Pixel-Qi Display. I heard a few negative things (the eInk-Layer should be slow and dark), but the videos I saw on youtube were ok. The biggest problem in my eyes is that actually there is no device with Pixel-Qi you could buy. And there is no way to get your hands on such a device - personnaly I don't believe videos too much. That they have great screens in the laboratories doesn't mean that this screens will hit the market.
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