Here are the differences between the ZG, EZ, and EZG:
The ZG is a playboat only, although it is really not that bad at river-running. For your height and weight I would go with the ZG 48; you are actually in a perfect height and weight range for this size.
The EZG is the new and improved EZ, and it is considered a river runner/playboat. The EZG has 3 sizes (42, 50, and 60 gallons) You would want the EZG50. Basically, Wave Sport took the EZ and improved the hull speed, length, and comfort factor(higher knee area) They made the EZG's a little shorter than the EZ's, which makes it a little better for cartwheeling, and spins in CO playparks.
The EZ is also a river runner/playboat; its big brothers are the BigEz, and the SuperEz. These boats are still good, and the lower price range makes it a great choice.
If you are an agressive paddler and wanting to do all of the aerial moves then the ZG is a good option. If you are just getting into the playboating thing and looking for a good boat to learn the basic playboating moves then the EZG would be the way to go.
I hope this helped.
Mark