Neither is better. They are, essentially, the same.
The speaker says that he comes to a fork in the road, and he examines one road and then the other. When he looks at the second, he says that it is "just as fair" as the first, and he claims that "the passing there / Had worn them really about the same [...]." In other words, then, the roads -- although they are not identical and do look somewhat different from one another -- have been traveled approximately the same number of times. To say that they have been worn about the same amount means that there simply isn't one road that has been more or less traveled than the other. They have been traveled equally. In fact, on the morning on which the speaker encounters the fork, he says that the two roads "equally lay" in the leaves, and so they are really not significantly different from one another. Therefore, when the speaker says that, when he's old, he's going to tell others than he took the road "less traveled by," he basically admits that he's planning to lie. Everyone wants to believe that their choices are significant and that they are original and unique, but, this poem suggests that there really are no such unique choices. They have all been made hundreds, thousands, of times before, and these decisions are really not as momentous as they seem at the time.
Thus, one road is no better than the other.