I'm not a fan of covers that are to be left on while you read. It makes the Kobo heavy and unwieldy in addition to making it hard to hold in one hand.
As my main concern is protecting the screen when transporting it in my bag or coat pocket, I am more than happy with this case:
http://cgi.ebay.ca/Borders-Kobo-eRea...item2a0edd2b08