I recently selected my next daypack - just waiting on my REI dividend check to go shopping! Being an engineer, I suffer from an unquenchable need to use spreadsheets and data. I set up a comparison chart of 5 models in my price range that all had the amenities I desired. One of the factors I used to narrow down the list was a ratio of capacity (L) to weight (oz) and I eliminated anything that was lower than 1:1.

While this is not the deciding factor, it helped me trim some of the fat off the list - why do I want a pack that weighs more than others yet has less capacity? As other respondants mentioned, fit is everything - so whichever of my final 3 feels best will be my choice. I am now down to the final 2: Osprey Rev 24 and the Camelbak Pursuit 24. What might tip the balance is that the Osprey is available on clearance for 50% off at REI. Might be too hard to pass up.

Good luck!