I would go with an older Sony PRS-650 or PRS-350. I have as well a PRS-T1 which has been far from glitch free. Lots of please waits or the reader application has stopped working or the revolving arrows that totally deplete the battery on occasion. My roommate has had the same glitches.
Expandable memory in a reader can slow things down and only really necessary,IMO, if you want to use audio books on it. I have 4000 books on my 350 and 4217 on my T1 (main memory only). I don't need that many books on at a time, but was curious as to whether it would degrade performance and can't see that it has.
If you like the kindle than that is good. I have had to return my mother's kindle twice because it kept restarting every few minutes. So possibly some kindles have glitches too.