I dont have a day pack but the Osprey Manta 28 is a good day pack from what I have heard and it has a hydration reservoir. You have a lot of options. If you are looking for something on the larger side for day packs make sure it s 25 - 30 liters. If you get anything bigger you start getting into backpacking backpacks. But there is a tons of options. Good quality ones are $130 or higher. You will want to get a large. I am 6'4 also http://www.ospreypacks.com/us/en/product/manta-ag-28-MANTA28_780.html