Which eReader?

The choice is yours! http://ebook-reader-review.toptenreviews.com/

The main thing to have in mind is when will you use yours.

For example, I stay up later than my wife and she doesn't want me to have the the light on, so the kindle paperwhite was excellent for me as i could read in the dark as it has a light on it.

The normal kindle which i think goes for 69 euros, doesn't have the light, so if you're just using it to read books on the train/plane, then it works just as well.

As far as the microSDcard slot, the ebooks aren't that big so that is really not a necessity since the device can usually already hold 1,000 books.

My other advice would be to make sure that you like how the pages are turned on the device. I'm not sure what brandname it was, but a colleague had one that it could only be turned by touching the screen. Might seem like a cool idea but with my device, my hands never really move as the page can be turn with a side button that is pressed when you need to "turn the page."

So the main thing is, will you be using the device for reading at night or not? And then maybe go to the store and see how the device fits in your hand and how the pages are turned.

My understanding is that the principle thing that matters is whether you can cope with an eReader at all.
I have 3 family members who own one and never use them. Two bought theirs and one was given his by a friend who had also bought one but never used it. At Christmas I shall be offered one for free providing I am comfortable with it.
Before spending your money, make sure that you are comfortable with using one.