Brother my favorite has always been and always will be the good old large ALICE pack. I slightly modified it so there's more padding on the kidney pad and on the shoulder straps. You can also add pouches to it if you actually want to use it for operational use. But just for rucking to get strong to train up for military life I would buy an Alice pack and get padding added to the kidney and shoulder straps if you need to. That's my go to