I'm stuck with a dilemma when I consider the pros and cons of lowering the drinking age.
dilemma a problem involving a difficult choice.
1. "the dilemma of "liberty versus order" —J. M. Burns
2. "She was placed in the dilemma of running all risks headlong on the next day, or of pausing for a future opportunity which might never occur."
3. "In Sophie's Choice, Sophie faced a dilemma in which she had to choose which of her two children would live, or let both be killed by the Nazis."
p.s. "on the fence", as suggested by Dan Bron, fits better because it refers solely to not being able to chose between A or B. A "dilemma" would be more appropriate if you really had to make a choice, like Sophie.