To all who replied - Thank you - with special thanks to those who listed models and pros/cons. I know it was a difficult question when I gave little info, but I have little info. I suppose I could/should have said - for the average user who lies within the central 40% of the bell curves of technical competence and reading material and price sensitivity and resistance to DRM and .... - what would you recommend that will work well with Calibre, but it wouldn't have provided much more info to base the recommendation upon.
I asked here as I didn't want anything that wouldn't work well with Calibre and because I know many names here, so could perhaps judge the replies better. If anyone has a brief "I like the gizmo better than my old whizmo because ..." I'd love to hear it. Thanks again.