using dd to copy my freebsd partion to another drive

[D Velez]

Hi, I would like to know what would be the best
block size to use when using the dd command.
I read many web pages on how to use the dd
command, but all have different block sizes
and I am confuse. I see some as bs=512 bs=1024
bs=8192, etc....

Is there a way to calculate the block size of the
two hard drives myself or is there a standard
block size to use for any hard drive, cdrom and floppy.

I appreciate your help

Thanks

David V