Hi Jho,
Are you still looking for an e-reader?
I agree that it is very difficult to choose.
And I also feel a bit resentful toward the industry because there are many e-readers, but none with all of the features that I would like. Instead-- like most things in life-- we must weigh the pros and cons and make a decision knowing that there is no perfect option.
However,
I would recommend against making your decision based on accessibility to book formats.
As Meera and Barry said above,
there is a free software called Calibre that you can use to convert book formats.
So book format is not something that you need to worry about.
Unless you are planning on reading a lot of technical or academic PDFs. Then you would want to choose an e-reader not by whether it reads PDFs, but how well it handles them. Same for if you were reading comics or manga.
For regular books, any e-reader should be fine.
Instead of format, I would focus on the following:
First, how will you get the majority of your books?
would you prefer to buy from the same store regularly and have books immediately available on your device?
or would you prefer to buy books from various stores and upload them to your device yourself?
What hardware features will matter most to you?
6" display, smaller display, or larger display?
front light, colour front light, or no light?
waterproof?
high-resolution display?
audio capability?
expandable memory?
cellular connectivity?
What software features will matter most to you?
text adjustability-- font, size, weight, paragraph style, spacing, margins?
page numbers?
additional dictionaries?
annotation?
web browser?
apps?
These are just a few features that may differentiate one e-reader from the next.
Consider how you will acquire your reading content, then consider how you will use your e-reader and which features will be most important to you for your personal use, and then choose the e-reader that best fits those needs.
In addition to the mobileread community, I find that watching e-reader review and comparison videos is an excellent way to learn about different devices. Just be aware that everyone has their own biases based on their personal preferences (which may not be the same as yours) and their past experiences (which can be very useful to learn from).
Good luck!
-sj