I would go with the Buck, then the Spyderco, and the Farmer last. Those little saws get very tiresome about the second inch of cutting. By the time you held onto those Farmer scales and cut a dozen or so saplings for a lean-to and/or firewood, your paws would be a mess. Great for one or two quick cuts.
Cutting green wood under 1-1/2" or so, it is easiest to bend it and cut on the outboard side of the bend and hack though what is left when it snaps off. Baton chunks out of larger stuff as you would with a hatchet. Given the inventory you chose, the Buck would do best there.
IMHO, swinging a short blade around like a machete when you are in a survival situation is a good way to fillet a needed body part-- not good. You will be tired, thirsty, hungry, injured, wet, cold, freak out or all the above-- not the best for fine motor skills
The point on the Buck equals the awl on the SAK. For general hiking, the Spyderco has the best horsepower to weight ratio. The Farmer would be just plain handy for cookin' and fixin' and lighter stuff.
Any of the three would be a darn sight better than none at all!
I hike with a Becker Necker and a mini multi tool like a Leatherman Micra or a (discontinued) Buck Mini. I am liking the idea of a Victorinox Trekker lately too. Mostly I have been lookng for a flat ground blade with a nice flat spine to whack with a baton. Serrated blades are great if you climb and might have to cut a rope, but I would prefer a good plain blade on the survival side-- easier to sharpen and less prone to getting stuck. Busse Game Warden, RAT-3, Striders and the like are on my drool list. Good simple lines, quality steel, hardware that holds up, and most importantly, it is there when you need it.