NIST GCode interpreters 3Axis v 6Axis

Hi,
Can anyone out there give me any details of the difference between
the two GCode interpreters used in EMC (apart from the obvious number
of axis supported!). I'm thinking of using this code as the basis of
a program I'm working on. Any advice as to which one is the best to
go for (I only have a 3 Axis setup so either would work). Is the
older (3 Axis) code still current?

Thanks

Andy