Reading device for College?

The review today of the Kindle Paperwhite reminded me of the fact that I desperately need a good reading device for studying. I've bought into the idea of 'doing it paperless' but right now I'm using a bulky laptop for reading, which is far from ideal. However, I'm still very unsure about what about device might be best in my circumstances.

The first choice is choosing between a tablet and an E ink reader. If it's going to be a tablet, it's going to be an iPad Mini - that's an easy one. The form factor is perfect for me and the ecosystem allows for a lot of other thing besides reading. However, does it really solve the main problem I have with my laptop, namely the screen? I'm doing a lot of reading in the train, with a lot of ambient light. I'm not really sure if the iPad Mini is suitable for that task.

If it's going to be an E ink reader, I'm not really sure what to buy. Let me give you a brief overview of my usage:

- I'm more invested into Google Play Books Store than the Kindle Store. Alright, I've only bought two books, but I like the look and feel, and pricing (until now) of the Google Play Books Store a lot more. It's also a bit more open than the Kindle Store.

- The files formats I'm probably going to use are PDF, EPUB and DOCX.

- I'm doing a lot of highlighting and annotating, so it's important that that works well.

- I store all my files on Dropbox so it would be nice to have that properly supported.

Of course, these are my personal preferences. How good the device itself is also comes into play.

That's about it. I'd love to hear your advice.