My first was a PRS-600 which I seldom use now because of the shorter battery life.
I was given a PRS-T1 as a gift with a lighted cover which I use for reading on the balcony. Not a big improvement on the PRS-600, if any, but the battery life and lighted cover are nice.
I had a PRS-350 which was for reading on the bus etc. but sold it to a friend in need and was going to buy another, but got the Kobo Mini instead, now my main ereader as it is the best to actually read on for me.
Will probably buy a Glo after Christmas, but who knows for sure
I read seperate books on each reader, not for any particular reason, but works for me.
Helen