Just so that someone answers this question, the answer appears to me to be no. It's possible that both those religions teach of a God that differs from the real one by precisely the same amount, but in different ways. Given that the description of God taught by a specific religion is finite, and is expressed in words, which have finite gradations of meaning, the probability of this outcome is non-zero, therefore one cannot be absolutely certain that it is not the case. It is also hypothetically possible, given a multidimensional but finite parameter space in which descriptions of God may be formulated, for there to be a real God, but for every religion's teaching of God to be inaccurate by precisely the same amount. Therefore, it is impossible even to be certain, in this hypothetical case, that there is any religion which gives a closer approach to an understanding of God than all others, let alone to form any kind of judgement as to which religion this might be.
Dave