I've also got an Aluratek Libre as does Mr. Pockets. I'm happy with the Libre as it has the 5" screen. You can also rotate the book to the wider length of the screen so it can be approximately 6" I'm guessing, never actually measured it. Also the adjustable fonts help a bit so you can determine what's best for your eyes.
The Libre is pretty light in my hands, I don't have any on hand experience with other e-readers so I can't offer an insight to weight comparisons. If that's a factor.
To me in my hand the 5" screen seems like a paperback in size, which is a rough estimate as I haven't compared side by side. Weight wise the Libre is a little heavier, depending on thickness, of a standard paperback. I don't really notice the weight over time, unless I actually switch from one to another.
I'd say go to Wal-Mart to see the Sony E-readers they have them and ask to hold one in your hand to compare the weight to a paperback. Grab one before you head to the electronics department for comparison. Also go to Best Buy if there are no B&N near to see a Nook. I think Best Buy also has Sony E-readers. You can at least see the size difference between them in store, but I'm not sure if they have actual models to hold, usually they're in a display case.
I think if you're an avid reader and depending on what e-reader you choose, you really can't go wrong with all the available options out there. Again depending on your preferences of what you want/need and where you shop. Hopefully this helps a little?