the trekker is the liner-lock model, and has a much beefier bottle-opener/screwdriver that I believe also locks. You also trade the corkscrew for a philips on the back. Overall its a touch heavier and tougher feeling knife, but having handled both, it pretty much comes down to if you want that tougher screw-driver.
I have the rucksack, and gave a trekker to a friend, we are both pretty happy with them.
One thought would be that if you don't like blade play at all, I'd go for the trekker. The slider lock on the rucksack is strong, but it feels more like a safety on a slip-joint than a lock, if that makes sense.
You won't go far wrong with either though.