There are some here who can tell the difference in the dpi - I'm one of them - and then there are some who claim that they can see no difference.
I 'buy into' both worlds: I have a Kindle and a Kobo.
You'll get fanatical responses, while some members here will give you a reasoned, calm response.
If you can, try both to see how responsive the units are for you.
Amazon - in my opinion - has the more responsive online store. Kobo is fine, though.
If you have any problems with Amazon, it's very easy to arrange for a return.
With Kobo - I have read here - SOME members have to be athletically inclined, able to jump through hoops of fire. (Since I'm a toad with a warty asbestos skin, I have no problems.)
I've had no recent problems with either units that I own.
I'm quite pleased with both, although my preference is with Kindle.
And finally, calibre is a friend to everyone.