1 leg is easiest to move around. 2 legs are more stable. 3 legs are super stable but hard to move. I have some variation of all 3 (a trekking pole with a v-yoke, a small extending bipod that is only tall enough to use while sitting, and a Bog Deathgrip tripod) and it really depends on the situation as to which I would use.
The Trekking pole is the most versatile, goes low enough to shoot from sitting on the ground, and goes tall enough to shoot from standing. But its also the least stable, and generally speaking I have my hiking pack on my back if I am going anywhere that I'm going to want a trekking pole, and I find the pack (with an internal frame for rigidity) makes a better platform if I can sit down behind it.
On the other end of the spectrum the Deathgrip is super stable, but its bulky and heavy, so you wouldn't want to be trying to move it around when its time to shoot. Would be great if you had a blind that you only looked in one direction from, but if you're looking out 2 or 3 sides of your blind then I would want something more maneuverable.
What about different sitting positions? I've found sitting cross-legged with my elbows on my knees to be a very stable position. Getting down on one knee and putting my elbow on the other knee has also proved useful, albeit less stable than crosslegged with both elbows supported. Also shot a bear from a folding lawn chair with my elbow on the arm rest, that worked pretty good too.