I've only ever owned a Kobo touch ereader and not used the kindle 4 much (I did have a brief try out with one a friend owns).
All in all I'm very happy with my KT.
I HAVE had it freeze up a couple of time. I think it was due to a dodgy epub I got from the Gutenberg project. A forced restart fixed it tho.
In some of the earlier earlier firmwares it would not recognise taps for page turning and then would suddenly turn 2 pages..
For the most part these issues are no longer a problem, the latest firmware (1.9.17) is pretty good for me.
The advertised support for 32 GB microsd cards is debatable tho. Anything over 2GB and many people have problems.
It sounds like I prefer the Kindle. Actually I by far prefer the Kobo Touch for the following reasons.
the KT supports epub (and many other formats) the Kindle doesn't support epub. WQhich means I can buy my ebooks from pretty much anywhere.
with the Kindle you're locked into the Amazon environment. (I do know there's ways around this, but for the average consumer, it;s probably beyond them).
No external storage with the Kindle. The KT support MicroSD cards. which is nice.