Ballot Box‘s Josh Goodman divides all of this year’s big-city mayoral races into the competitive and foregone conclusion categories, but he finds Boston’s to be the most unpredictable:

The toughest case is Boston. There’s a reason that Thomas Menino is sometimes called “mayor for life.” He’s been mayor for 16 years, winning reelection easily three times. In the most recent poll of which I’m aware, he scored a 73% approval rating.

On the other hand, he has well-funded challengers. The e-mail investigation into Menino’s administration might or might not be a big deal, but it has at the very least produced some unflattering press for the mayor right before the election.

The all-candidate primary will take place next Tuesday. My guess? Menino wins easily. However, this is one that I’m at least going to keep watching.