Understand that these are mutually beneficial agreements. I choose to endorse these products because they are the best on the market. The products are not the best on the market because I'm choosing to endorse them. Quality is quality no matter what.
With that said, here is my choice for April:
Marmot's Eiger 35 Pack
I love this pack because, as a climber, it is the perfect size. With a volume of 35 liters, I can fit a 60 meter rope, a full rack of 14 or so cams, half a dozen quickdraws, several pairs of climbing shoes, chalk bag, harness, food, water, and a few extra layers of clothing. I can even lash a thermarest and a lightweight tent to the sides of the pack. No problem. I've used it to approach Half Dome with 35 pounds of stuff as well as for day trips looking for new problems. The compression molded back panel molds to fit your back perfectly while the S-curved shoulder straps and the thick waist belt help distribute the load however you like.
Additionally, the Eiger 35 has a hydration pocket for your water bladder, stash pockets in the waist strap, a solid closure system for the lid, and above all, its COMFORTABLE.
It's the only pack I own for all of these reasons. If I'm packing lighter, I'm wearing a crash pad, otherwise, it's the Eiger 35. To check out the true technical details of this pack, visit http://www.marmot.com/