The Tony Allen vs James Posey debate rages onward.
It really is apples and oranges in some respects.
1-James Posey is not the same player as Tony Allen offensively. He is primarily a Long range shooter vs primarily a slasher. Entirely different styles of play that will both result in points on the board. Tony shoots the higher percentage type of shot for the most part.
2-James Posey is 6-8 while Tony Allen is 6-4 with thick soled sneakers on. Posey is a natural SF who can play multiple positions due to his length and strength. Tony is a natural SG who plays multiple positions due to his speed and quickness.
3-James Posey is the more experienced player who knows when to foul and when to back off. His mental participation in the game is superior to Tony Allen's at this time and may be superior to our own big three in some respects. This is the primary benefit that Posey gave us last year and is the reason he commanded so much more money on the FA market IMO.
To expect Tony to replace Posey as a backup SF is like expecting him to play PG and likely will yield the same results. Expecting too much of Tony will just lead to disappointment. I think it is unfair to Tony Allen as well. 
TP4U, very well said all around and some great points.
I think you're 100% right about Tony Allen and his positioning. He's a SG and that's where he will be most effective and hence, really won't be making up for any loss of Posey. I really hope that Tony can give us what he gave us last year but only during more meaningful minutes and with more consistency. That is how he will help this club the most.
It's when Tony tries to do too much or things beyond his limitations that he gets in trouble. I hope he plays within himself and just becomes more of a constant and so much less of a variable.
I do not disagree strongly with anything stated in the Tony Allen vs. James Posey debate. But I think there are a few vital points missing here:
1. The original question was whether the Celtics are better this year.
2. Last year's team had both players.
3. Even more importantly, last year's team played Posey far more in the playoffs than TA.
4. Ergo, Posey must have been better FOR THIS TEAM than TA last year.
5. Summing up the above, having TA take Posey's minutes next year is a weaker team.
First, you can logically disagree with this if you think TA will be much improved next year because his knee will continue to heal. I do not take this position because it is too unproven, but it is logical. Otherwise, I think that the Celtics last year, for this team, valued Tony Allen more therefore, giving TA Posey's old minutes cannot make for a better team.