The Heat and Celtics have engaged in a heated rivalry since LeBron James and Chris Bosh joined Dwyane Wade to shape the new Big Three -- joining forces just three years after Ray Allen and Kevin Garnett aligned with Paul Pierce as their predecessors and inspiration.

Allen will be called a ring-chaser and labeled gluttonous for leaving the Celtics in favor of the Heat, but in actuality Allen only opted for greener pastures with a better chance at another championship. In many ways, he did what we all insist we would do in the same position. If he found it hard to be loyal, why not play for a team that has a great shot at winning it all?

Allen will sign a contract with Miami that will be worth a fraction of what he could have been able to sign with Boston. He’s agreed to play basketball for less money and it was clear from well before free agency began on July 1 that the Heat wanted to add him to their arsenal. It’s not as though he called LeBron and Wade begging them to get him a job.

Grade for Allen: A-

There is something to be said for loyalty, but playing for the Heat should extend the effectiveness of Allen’s career, which some declared dead in May. Allen was playing on a badly injured ankle -- he’ll never admit how bad it was before surgery -- and a shooter of his caliber simply doesn’t forget how to hit the bottom of the net. He’s also in better cardiovascular shape than 99% of the league.

With LeBron and Wade penetrating into open space as Bosh spreads the floor in the mid-range, Allen will be the recipient of many an open three. If not, his presence will make things easier for his predecessors as a moderately-paid decoy. He’s the greatest perimeter shooter of his generation in an offense that is nearly unstoppable when the supporting cast is hitting shots (see Game 5 of the 2012 NBA Finals).

Grade for Miami: A+

The benefit for Erik Spoelstra and Co. is two-fold. Not only are they adding a dangerous perimeter threat, but they are taking a clutch shooter away from their biggest adversary. 

Allen is one of the most respected players in the NBA and in six years covering games, it’s impossible to think of a star that is more professional. In a locker room full of surly personalities, he made time for the media and seemed to genuinely enjoy conversing. If you look in the archives of any major Boston newspaper over the last five years, I guarantee that Allen is quoted more often than anyone not named Doc Rivers.

Grade for Boston: C-

The Celtics began preparing for Allen’s departure when Avery Bradley received more minutes as the veteran’s ankle barked. Bradley was so effective in the starting lineup, bringing a stronger defensively presence, that Allen was moved to the bench when he returned.

Rivers will soon find that Bradley isn’t nearly as reliable as Allen -- at least not yet. He isn’t going to garner the same level of defensive attention, making things harder for Pierce, Garnett and Rajon Rondo.

Ah, Rondo.

It was evident in Boston that the relationship between Rondo and Allen was souring long before national reporters began citing it as a reason why the latter might leave. I don’t know the exact reason why the pair didn’t get along well, but there are a number of plausible reasons.

Rondo is a moody player so perhaps Allen tired of his antics. Rondo may have preferred playing with the younger, more athletic Bradley on the perimeter. Maybe Allen resented Rondo’s increased responsibility and profile in Boston -- going from the Big Three’s plus-one, to the fourth member of the Big Four, to the best and most important player on the roster. We may never know.

Allen is also believed to be upset about a near-trade to the Grizzlies before this past season’s deadline. That may have been the third strike in his mind.

As much as people in Boston don’t want to hear it (take a look at some of the tweets from Boston writers/reporters on Friday night), there were only a few places that made real sense for Allen and Miami was tops among them.

Allen wanted a three-year, $27 million deal from the Celtics, according to the Boston Herald. If the report is accurate, he wanted the same respect and loyalty from the organization that Garnett received just a few days ago when he agreed to a new contract worth $34 million over three seasons.

If his deal with Miami is for the same length, he’ll make a total of $9.5 million. He was content enough leaving Boston that it would have taken three times as much money to keep him in green. That says more than anything he could admit to the media.

Danny Ainge wasn’t willing to meet his request, so the next best option was to sign with the Heat. The weather is nice, he can play golf even in the winter months and Pat Riley made him feel wanted during their brief courtship.

Here’s the head-scratching part for me. Ainge is reportedly going to give Jeff Green a contract in the neighborhood of four years and $40 million. If management is signing off on that type of contract, are you telling me that they wouldn’t sign off on a $27 million deal for Allen?

The Celtics may not regret letting Ray Allen go immediately, but his absence will be made abundantly clear when Avery Bradley struggles from deep and perhaps even when he hits a fourth quarter dagger for the Heat next May in Boston.

When he jogs back down the court with his fist clenched and arm swaying at a ninety degree angle, the Celtics will be sporting green on their jerseys and envy in their eyes.