Opening in Gmail is the easiest for me, as I don't have desktop email clients configured.

Just send the .eml files as attachments to yourself in a gmail or gapps account. When you click the attachment preview on the received message, it pops out a window displaying the email rendered as if it was sent/received in gmail. Includes inline MIME images too. You can print rendered pages from there.

I found this feature pretty neat! And a bit unexpected.