I own and use both depending on the trip. Lumbar is the way to go for ease of use, comfort and a dryer back. I recently purchased the new Osprey lumbar pack (seral), Its got a 1.5 liter bladder and room for tools, snacks and a jacket (a must for summer alpine rides in Colorado). I also use a water bottle in the frame and can easily do rides of 40 miles with water to spare. I also owned the Evol lumbar pack but returned it because of poor bladder design and it was just a bit to small for my needs.
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