I adore Kelli, and I think her work in BRIDGES is grade A quality. However, I am personally hoping for Menzel to win. I know she has already had her "time" as some others have put it, and that Kelli is overdue (which she is,) but many didn't question the turnout when Audra won her second or third Tony lol.
Also (and I want to tread lightly because I do NOT want to discredit Kelli's work at all, she is working her @$$ off every night for a show that is sadly sinking,) but Menzel is playing a role that is unlike any role to ever come to Broadway. She is essentially playing the same character, but playing her two different ways at the same time. She never leaves the stage (and she she does, its very brief) and the vocal demands are high. The show might be written around her voice, but that doesn't make it any easier to sing eight times a week.
I definitely see it being a nail bitter if BRIDGES stays open till the Tony Awards though. It is kind of rare to have a season where two Broadway veterans who are both loved by audiences and critics alike and are making career defining roles be put into the same category.
"Life in theater is give and take...but you need to be ready to give more then you take..."