Baron,
I think you need to provide a bit more information on what you are trying to cut.
A while back i did a "saw-off" where I was comparing a Bahco 396-HP folding saw (the same as the laplander build to cut hard/dead wood, as opposed to the 396-JT which is for soft/green wood), an Unbelievable Saw (made by Supreme Products, who also make the Pocket Chain Saw - the only difference is in the handles), an 18" Trailblazer Take-down Buck Saw, and a Sven Saw.
My favorite of the bunch, by far, was the 18" Trailblazer Take-down Buck Saw. It went through wood like butter and the round handle was VERY comfortable in use. Also, when stowed away, the round tube is "easy" on the other gear (unlike the Sven Saw). Its only disadvantage is that it does take a little time to assemble, but that goes much faster as you get used to it. I also like that there are no small loose parts that can be lost (the wingnut can't - and doesn't need to - come off the tension rod -- unlike the wingnut on the Sven Saw).
To answer the earlier question - the Buck Saw comes in two sizes - 18" and 24". The 18" one worked fine for me, though if you have the room I would guess the 24" one would cut faster with the longer stroke. I'll also mention that I was a bit worried that the teeth on the saw blade would be damaged from rubbing up against the tubes when stowed away, BUT a friend of mine who works in a metal shop assured me that the heat-treated teeth are much harder than the aluminum tubes, and would not be damaged.
The Sven Saw was my next favorite. It cuts as well as the Buck Saw, but the handle isn't as comfortable (too thin) as that of the Buck Saw, and the package when stowed away is sharp enough to damage gear (though you might be able to grind down the sharp corners without any harm). The other issue is that it is a pain to install a new blade since it uses a split rivet that has to be punched out with a tool (flattened nail), whereas the Buck Saw has a loose blade. I should mention that there is a wingnut on the Sven Saw that could easily be dropped and lost. When I took it to the Boundary Waters years back I brought along two extra nuts - just to play it safe.
The Unbelievable Saw cut incredibly well - as good or better than the above-mentioned saws since on 4-5" branches it actually cuts three sides at once. The plastic handles are great - very comfortable, and the whole thing packs as small as the Pocket Chain Saw. Note that the first page on their website suggest it comes in a large blister pack, but in reality it comes rolled up in a nice small heavy duty zip pouch. BUT when cutting horizontal wood I would have to saw from the side, and EVERY time I did that the weight of the branch would come down on the bottom part of the saw and the saw would get stuck. Every time I found myself having to break off the rest of the branch while hoping the chain saw didn't break. I tried cutting from the bottom up, but it was difficult to do. I've heard some people complain that the hook on the Pocket Chain Saw coming undone, but it seems that would be very fixable (fold it a bit more).
The Bahco 396-HP cut the slowest, partically because of the length of the blade (7.5"). It was my least preferred of the bunch, though it certainly packs the smallest and is when stowed away is rounded and very gear-friendly.
Sometime I'll need to put them on a scale and see how much each weights.
Links:
Trailblazer Take-down Buck Saw:
http://www.trailblazerproducts.com/
Sven Saw:
http://www.svensaw.com/
Supreme Products Chain Saws:
http://www.supremeprod.com/
