This is just my experience and may not be what you have in mind but here goes. I've had pretty good luck useing standard oval or pear shaped aluminum biners sectioning out limbs and logs up to about 200lbs and had good luck dragging up to about 1000lb logs and brush out of ditches useing a skidsteer. I agree with the post above that steel would be better for rigging it's just that I normaly use old aluminum biners for rigging. Matter of fact I've had 1/2 rigging/old climbing lines snap long before the biners showed any stress, however the lines normally snap on a knot where the strength of the rope is greatly reduced.
I like useing a biner instead of a running bowline as a choker just because I can do it one handed and a lot quicker, however it makes it harder for the groundsman because the knot and biner get hung up when they try to fish the rope back out of the brush pile or lowered limbs.
Also I spray paint the biners so I know they are not for climbing use. Good luck.