Whats the difference between these two similar sized and weights bags? Well both are from the Lite range and both have the same weight of 350 grams or 12.3 ounces. The Ready Pack is 18L in capacity though while the Lite Daypack is 20L.
In my testing I found that the Lite Daypack was very comfortable to wear and did have a few less features overall than the newer Ready Pack. Most notably is that the Ready Pack has an external water bottle pocket and a larger front stash pocket with internal pockets. While the Lite Daypack only has a slimmer stash pocket on the top and inside the main compartment with a few additional stash pockets that aren't as big. Both have a laptop/document sleeve down the back and both are very comfortable to wear for extended periods of time while fully packed.
Both bags also have a nice minimal sternum strap that has 3 levels of positional adjustment but get the job done sufficiently and I found them comfortable and easy to use. The Lite Ready pack has a nicer grab handle on the top whereas the Lite Daypack only has a thinner more standard loop of webbing material for its strap. Overall if I had to pick one I'd probably lean towards the Lite Ready pack because I like the external stash pocket and its overall design. However the Lite Daypack is probably better if you were going to use it an an only one bag. The Ready Pack is better as a packable daypack but both do the job well.