I'm sold on the running vest style straps with bottle holders, and bottle pockets on the side of the pack. Here's a custom pack I ordered for extended day hikes (like Mt Whitney or San Gorgonio), designed to carry two 1L Smartwater bottles in the side pockets and two 700ml Smartwater bottles (with the sport caps) in the vest pockets:
On Mt Whitney I always filter water, I've seen wag bags, feces, and discarded shart filled undies near water sources and don't want to take any chances. For a day hike on the main trail I'll fill up all the bottles at Trailside Meadow which should get me to the summit and back down the switchbacks. With the bottle locations and the filter in the exterior pocket I can do the filtering efficiently without having to open the pack and reach inside.
Was super fit like a month ago but work has gotten in the way and that is screwing up my plans to train for another Whitney day hike. I've got a backpacking permit for the Shadow Creek trail later in the summer so will hopefully be able to do one or both.