I would use a weld on type that the shackle connects dirrectly to...less parts to fail!
For bolt on I would use something like this
and have a solid plate behind it sandwiching the bumper material. This will help prevent the bolt heads from pulling through. Might be overkill but better safe than sorry!
And I am pretty sure you said you were doing so but just incase...high quality grade 8 bolts ONLY!