I only have three eink readers. The Sony PRS-500 because it was the only thing available at the time. The Cybook Gen3 because I wanted dictionary capability and ability to read Mobipocket. Sony was the only source to purchase LRF books at that time and PRCs were widely available. The EZ Reader when my Cybook seemed to die and I panicked.
Of them all I read the EZ Reader most often and occasionally the Cybook when the EZ Reader is charging. My daughter inherited the Sony.