While I agree atm Parker is better than Rondo, I think it is closer than some might believe. Parker is clearly the better offensive player, but virtually a no show on defense. Offensive statistics are easy to quantify, yet defensive impact is far more difficult to measure.
This is abundantly clear when you have a guy like Battier on your team and you constantly have to argue with idiots on clutchfans as to why he is an integral piece despite being a below average offensive player. But I digress....
The question becomes: is Rondo's O + D > Parker's O + D. The answer is almost impossible to answer. But a pure statistician might argue that since both Boston and San Antonio have tons of offensive weapons, the player who brings more to the table in versatility is trully the more the valuable player. A counter arguement can be made however that when a team faces a lot of injuries, such as the Spurs last year, the player who can step in and fill that void in scoring is the more valuable player. So I think it is fair to make a case for both players.
And the ring arguement is just silly. Teams win rings, not players. Anyone who tries to use that criteria when rating the quality of a player does not make a good case, because of all the other variables in winning a championship.