My Grizzly model is quite light and easily light enough for me to use for a 1 to 2-mile hike. I don't know what your physical abilities are, but if you're near average in that regard, you'll have no trouble packing a Watermaster Grizzly. If you're going overnight though, you'll have a pretty good load between your fishing tackle, overnight gear and your raft -both in weight and bulk. If you wont be going more than one or two miles, physically able and wont be staying more than a couple nights, the standard Grizzly model might be best. The lightweight model is significantly more expensive and, as I said above, probably less durable. There's also the question of how easy the material is to patch when (not if) you need to make a repair.
The dry bag/backpack that came with my Watermaster is large enough in size to carry other items, e.g., fishing gear, etc. besides the raft/oars/pump. My friend's Kodiak model comes with the same dry bag and, being larger, consequently has much less room in the bag to carry other gear -another advantage besides the lighter weight and lower cost.