For my money, it would be one of the etrex legend or vista series, a late-ish colour one, because they have the battery life for a 200 or even a quick 300 on AAs, and you can get them second hand for less than a whole arm and leg. Mine's a legend Cx.
Edit - The only time I had a problem with switching off, I sorted it by buying a mount that wasn't broken. It was bloody annoying at the time though.
Edit-edit- Wot e sed about HCx. I can't keep up though. I'm hitting post next time whatever it says about new replies.