Bantam is reference to the overall *SIZE* of the chicken... Many breeds come standard (large) and bantam (small), while other breeds are either / or.
If memory serves (and it doesn't always LOL) I seem to remember reading there are more bantam varieties than standards... but that's counting all the color varieties even within single breeds. The Old English Game bantam has well over 100 color varieties alone (again going by memory, so if I'm wrong someone please *gently* point it out?
Most bantams average 2 pounds or less, while standards can be anywhere from 4-10 pounds depending on the breed (some a bit more some a bit less)
Now the cochin, for example (my favorite)
- the Large - Cock: 11 lbs, Hen: 8 1/2 lbs.
- the Bantam - Cock: 30 oz, Hen: 26 oz
Hope that helps...