Re The textual problem μονογενὴς θεός (“the only God”) versus ὁ μονογενὴς υἱός ( “the only son”)
"It seems to have arisen from a confusion of the contracted forms of writing, Υ and ΘC. The question, which reading to adopt, is one which, in the balance of authorities, must be provisionally decided by the consideration that as far as we can see, we should be introducing great harshness into the sentence, and a new and strange term into Scripture, by adopting θεός: a consequence which ought to have no weight whatever where authority is overpowering, but may fairly be weighed where this is not so. The “præstat procliviori ardua” finds in this case a legitimate limit." (Alford).
Scholars who opt for υἱός consistently point out the apparent isolation of θεός in the Alexandrian form of text. In fact, Ehrman argues that because “virtually every other representative of every other textual grouping—Western, Caesarean, Byzantine—attests to υἱός,” θεός does not “fare well at all." (Wallace)
In any event those who opt for μονογενὴς θεός (without the article) - these being the Trinitarian hardliners who credit "God the Word, God the Son etc" (and who first arose in some of the successors to the apostles) - are put into the position of having to disapply Sharp's rule to θεός, as they must accept their own biblical intepretation that θεός is μονογενὴς. Or is it that they are greedy and want to have their cake and eat it?