The Introduction to Nestle's Greek New Testament, Novum Testamentum Graece, cites the use of Aleph & B as the basis for its text saying"....the precedence of the Vaticanus will be justified."
(Religious Thought in the West., pp. 2, 7, 12.)
There are critics that don't agree with this. Dean John Burgon was more than able to comment on the subject since he had done extensive hand collation of major uncials, Aleph and B. included. This is what he had to say:
"What does astonish us, however is to find learned men...freely resuscitating these long-since forgotten critics [Aleph & B] and seeking to palm them off upon a busy and careless age, as so many new revelations...t is sometimes entertaining to trace the history of a mistake which, dating from the second or third century, has remained without patron all down the subsequent ages until at last it has been taken up in our own times...palmed off upon an unlearned generation as the genuine work of the Holy Ghost. What...of those blind guides...who would now, if they could, persuade us to go back to those same codices of which the church had already purged herself." (The Revision Revised, pp. 94, 151, 334-335)
Dr. Wilber Pickering says about Aleph & B:
"To judge by the circumstances that codices like Aleph and B were not copied, to speak of, that the church by and large rejected their form of text, it seems they were not respected in their day...If readings...died out in the fourth or fifth century we have the verdict of history against it...They [Aleph & B] are remnants of the abnormal transmission of the text reflecting ancient aberrant forms. It is dependecny upon such forms that distinguishes contemporary critical editions of the NT...Their respectability quotient hovers near zero...In particular, I fail to see how anyone can read Hoskier's Codex B and its Allies with attention and still retain respect for Aleph & B as witnesses to the New Testament...The modern critical and eclectic texts are based precisely on B and Aleph and other early manuscripts...They have been found wanting...The result will be the complete overthrow of the type of text currently in vogue. (Wilbur Pickering, The Identity of the New Testament Text [Nashville; Thomas Nelson Publishing Co., 1980], pp. 120, 136, 145, and back cover)
Dr. Herman C. Hoskier's extensive collation of Vaticanus (B), unsurpassed to this day, leads him to conclude that the new version editors are guilty of an "...incomplete examination of documentary evidence...[working] without due regard to scientific foundation. He says:
"My thesis is then that B (Vaticanus) and Aleph (Sinaiticus) and their forerunners, with Origen who revised the Anitoch text [KJV], are Egyptian revisions current between A.D. 200-400 and abandoned between 500 and 1881, merely revived in our day... (Which Bible, pp. 134-143)
Harvard and Princeton textual scholar, Dr. Edward Hill says:
"Old corrupt manuscripts, which had been discarded by the God-guided usage of the believing church were brought out of their hiding place and re-instated...and today thousands of Bible-believing Christians are falling into this devils trap through their use of modern speech versions." (Edwrad Hills, The King James Version Defended (Des Moines Iowa: The Christian Research Press, 1973).
"why are such old exemplars even still in existence and in the relatively good condition which they are, since they are over fifteen centuries old?" The answer suggested by numerous scholars such as Van Bruggen, Pickering, and others is that these scrolls are in good condition despite their age because they were never used. They did not endure the repetitious unrolling and rolling back up, the assault of sweaty hands and humid breath, the violence of tears and bends that come from constant use. Simply put, these exemplar manuscripts may have simply sat upon a shelf for most of their long lifetime. The next question becomes then: "Why?" The answer, logically, is that they were probably rejected from use by early Christians who understood them to be flawed, and refrained from relying upon them. Exactly this argument is presented by textual scholars including Van Bruggen.(See J. Van Bruggen, The Ancient Text of the New Testament, pp. 26-27).
It may surprise you to know that B differs with Sinaiticus Aleph according to the 500 page study by Hoskier which detailed and discussed the errors in Codex B and another 400 on the idiosyncrasies of Codex Aleph, Sinaiticus Aleph and Vaticanus B were found to differ from each other in the Gospels alone 3,036 times-not including minor errors such as spelling or synonym departures.