Another vote for the tri-blade. It is an absolute monster in thick field grass and brush up to 3/4". I can sweep it up and down to face the brush encroaching on my driveway and
use it like a scythe in low brush and grass.
It doesn't cut thick brush as well as the circular blades but spools up a lot quicker.
I use it without the guard(I know, I know) so I need a full face shield. It slings stuff everywhere.