I'm a little confused. You state from "my experience that a Kindle is inferior to a Kobo". Doesn't that already mean you already know why?
Honestly, there is no way I would categorically state one was inferior to the other. They both do things the other doesn't (email books to Kindles and have them sync, Kobo does series info and collections can be managed). They both do some things better than the other (more font/reader settings in Kobo, better dictionaries in Kindle).
From the list of things you mention:
- Reading fiction - The real differences here will be in the navigation. Both are perfectly capable of displaying text to the screen in a very readable way. The problems now tend to be badly formatted books, which both will suffer from. There is a difference in the reading settings (fonts, size, margins and line spacing) but, how often do you actually change these? And unless you have real bad luck and what you want is exactly in the middle of what is available, you will probably find something suitable.
- In-built dictionary - It is well accepted that Kindles have better dictionaries. But, if in your use of your Kobo, you have never not found a word, then a better dictionary isn't useful.
- Note taking and highlighting - both do it. I have no real issues with how it is done on a Kobo, except that I the actual highlighting can be a little slow, so I just need to be careful. I've never tried these on a Kindle, so I don't know.
- Goodreads and X-Ray - Neither are available on Kobo's, so the only choice is a Kindle if they are something you want. I don't actually know what Goodreads function a Kindle supplies, but if you just want to sync your reading status to Goodreads, then you can do this with a Kobo via calibre.
Personally, I am firmly in the Kobo camp. On the occasions I have used a Kindle, I have found it a frustrating experience. But, how much that is to do with how well I know the Kobo UI and little I know the Kindle UI, I don't know.
And, as @Sirtel sort of implies, if @JSWolf chimes in, just ignore him. Or tell him that you think Nook's are the best ereaders ever produced.