ERISS: That's wrong, PR has more units.
MA is like a demo of PR and it's a shame that it's sold 10$: we could buy those many unsold MA 3$ in stores 5 years ago..
So, to answer:
don't buy MA, buy PR which is better on all.
Lord_Kane: which units are new in PR? I am curious now. I have to confess that I only played MA very briefly at a friends house, and bought Domination (as its known here in Canada) on impulse and did not discover the two where related until I realized that Domination/Massive Assault was made by wargaming.net when I started to get into World of Tanks.
PR
is Domination under a different title. The two sides in PR have additional unique units to shake things up. The Phantom League gets giant superunits that can attack twice per round, the FNU gets sneaky units that enable flank maneuvers. Play the scenario "the jump" for an example of this.
All that said, I don't know that I can recommend the gog version right now as it's apparently crashing all over the place due to missing files. The gamersgate version is complete, albeit still prone to CTD on the Oribtal Station Thunder map.