The Southard is 4.5" long when closed.
Both of the others are less than 4" closed.
I cannot hang onto a folder that is less than about 4 1/4" closed, as I have large hands.
So it depends on your hand size. I love Sebbies, but when I try to close a small Sebbie, my hand must naturally slide back on the grip a bit to use my thumb to depress the frame-lock...and the knife slips FORWARD out of my hand.
So, now it's either one longer knife...or one of the two shorter ones. If you can hold onto a small Sebbie, and lots of folks can, then it is the best knife by far, for you. IMO.
I've owned two Southards and many small and large Sebenzas. I've studied and admired the "mini-Sam" but it's too short in the grip for me...very similar in grip-length to the small Sebenza. I do like the Sam's blade design and thickness and would try it if I had a smaller hand.
I have purchased quite a few small Sebbies in the past just because they are so beautiful. I have never carried one. I always sell them again after a couple of weeks. The inlaid wood Sebbies, or leather-inlaid models, are wonderful, as is the box elder, and on and on.

ANY Sebenza will last you forever. IMO, there is NO competition. Different strokes.