I'm a big fan of the Nine Trails pack for how lightweight and comfortable it is. It fits really well and the hip straps take a lot of weight off of my shoulders - plus the strap pockets are a great place for snacks.
I took this pack with me while backpacking Mount Timpanogos and while it was super nice to have for my sunrise summit, it's not ideal because it doesn't pack down small into my bigger backpacking bag. Other than that, though, this is a great day pack. The mesh side pockets are big enough to fit a Nalgene, and tight enough that it won't slip out if you bend down.
This pack also functions well as an everyday bag, it has plenty of room to fit a laptop, lunch, and some books or layers. From midterms to mountains, this bag's got your back both in function, capacity, and style. There are some solid color options and it has a very clean look.
What I carried in the pack:
Timpanogos Summit (full pack): crampons, nalgene, trekking poles, DSLR camera, an extra layer, a beanie, my headlamp, a knife, a couple snack bars, hand warmers, gloves, and a sandwich.
Day hikes (half full): same as above, minus the camera and crampons.
To work (half full): a notebook, lunch, nalgene, sunglasses, jacket, snacks, workout clothes