If God's word is all truth and God speaks through his prophets, then it doesn't matter which prophet God prefers.
If a prophet delivers the word of God, that word is truth.
All the prophets are good and honest in telling the true God's word.
If God prefers Prophet A more than Prophet B, but both Prophets words are truth, then God's preference isn't relevant.
God's preferring this or that, is only about giving that prophet his own reward and his own rank.
But If God prefers Prophet A more than Prophet B, and so the words of Prophet A are more true than Prophet B, then Prophet B would have to be partial lies or deception. But that means God deceives through his word, which I doubt you believe.
God's preference of any prophet is according to his striving, his degree of faith and his good heart; it does not mean any prophet is a liar.
Example: Prophet Mohammed: he conveyed the word of God .. once he forge any word of his own, or he adds any word saying: God said this to me while God did not say that .. then God would curtail the revelation and take the prophecy from him and punish him a double punishment in the life of the World and the Next Life.
Moreover, the prophet himself knows very well that God will punish him should he forge any lie of his own words.
Quran 69: 43-48, which mean:
43. [The Quran is] a revelation from the Lord of the worlds.
44. And if [Mohammed] had forged and attributed any sayings to Us. c
45. We would certainly have taken away [the revelation] from him by force,
46. Then We would have stopped the [continuous or the going on] revelations to him. d
47. Nor could anyone of you e have kept [Us] off from him. f
See more explanation in the link:
http://quran-ayat.com/pret/69.htm#a69_44
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quran-ayat.com/pret/69.htm#a69_44>