My tractor has a pretty high lift capacity, far more than will likely ever be tested by with a grapple by me, particularly as there are few really big trees and I have no intentions of cutting them. Most of my land clearing involves 0-6" trunks; for me it's more a matter of volume.I've owned two styles of grapple.
Don't get hung up on jaw opening dimensions. My old single lid clamshell root rake had a wider opening but my long bottom twin lid grapple will grab twice as much brush and pick and handle heavier loads than the clamshell ever could.
The long bottom grapple has a big advantage of grabbing brush from further away from your radiator grill. That might actually be a minus on smaller machines with limited lift capacity.
The long bottom is also better at grabbing piles of logs. It will also carry larger bunches of logs than the single lid clamshell ever could.
If you have limited lift capacity the single lid clamshell is going to work better for your machine. Grabbing more is meaningless if you can't lift your grab.