As Scott Rubin noted below, the vast majority of known Maryland Fourpence are of the Large Bust variety. The easiest way to identify this type is to look for a hyphen between TERRAE and MARIAE; the presence of a hyphen is diagnostic of the Large Bust. Late states of the die show the reverse starting to break down on the right side of the shield; advanced states show a large lump of metal connecting the shield with the V of the denomination.
Mint State Maryland Fourpence are exceedingly rare. The finest appears to be the NGC MS64 from the Donald Partrick Collection. A close runner-up is the impressive double struck PCGS MS62 which shows a strong rotation between strikes.