The photo of the clevis shackle that Bart posted, is also known as a bow shackle down under.
They are the best because they -
Are made from higher tensile steel than a normal shackle, so are stronger for the same size.
Give more room for the strap to go through, and do less damage to the strap.

I always use a snatch strap, even for towing on the road.
You just adjust the length of it to suit.
It takes all of the jerking out of the towing connection that occurs when a normal strap goes slack and then tight again.

Just my preference though - others will have different opinions and experiences.

Bart's explanation of a snatch block in use is good.

PK