I was a big fan of the Whisper, and still enjoy mine. But I bought a Murmur because it added the two things I frequently found myself wishing for on the Whisper, namely the side pockets and the sleep pad pocket. Of those two, I find I like the sleep pad pocket the best. Either my GG Nightlight or my BPL Torsolite fits fine, doesn't slide around, and provides very adequate padding and stiffening for SUL loads.
The resulting pack is as those two guys in the Guinness ads would say, "Brilliant!"
I must say that the stock waistbelt was too short to encompass all of my midsection, prompting me to both go on a stricter diet, and buy a larger strap to replace the factory one. All joking aside, I've never had that problem with other light packs, like my REI Flash 18; why is GG so skimpy on the waistbelt length? A few of us are not wasp-waisted hyper-milers ya know!
Other than that very minor complaint, I love my Murmur and everything else that comes from Gossamer Gear. It's all first rate!