Buck 303 Cadet is a sturdy tank of a knife. The Case version is their '44 pattern, 6344, which is slightly slimmer to carry because it uses 2 backsprings versus the Buck's 3.
The Buck pattern has the sheepsfoot blade hinged opposite the clip. blade. This results in a longer and thicker blade than the Case. Also, when using the main clip blade, I find that the Case sheepsfoot sits proud as they usually do, and the spine of it presses noticeably against your middle finger when firmly gripping the knife. On the Buck, the Sheepsfoot sits lower, and right beside the modified spey, so it's not noticeable. It's much more comfortable to hold the Buck knife firmly with the main blade open.
In general all of the blades on the Buck 303 have thicker spines, and use a saber & hollow grind, whereas the Case knives use a continuous hollow grind.
The result is tougher but thicker blades on the Buck, and thinner more graceful blades on the Case. It's really the most noticeable on the sheepsfoot blades. The Case blade is a thin scalpel-like slicer. The Buck is more like a sturdy utility-knife blade.
If you want a sturdy working tool, I'd go with the Buck. For a more lightweight carry with blades suited better for slicing and more delicate work, I'd go with the Case.
Another option if you want to go up a notch is the Queen #26 small stockman. It's also 3 1/4" closed and gets you D2 steel. I've never owned or handled one of those so I can't really comment.
Actually, everything you need to know about the Case versus Buck is in this thread:
http://www.bladeforums.com/forums/s...03-to-Case-Medium-Stockman-(Dark-Red-Bone-CV)