I've only read the first and last couple of pages of the thread, but it seems the bottom line is that if we discount the attributions by 2nd century Christians we can't really know who wrote the fourth gospel. Most of the arguments back and forth are highly speculative and very weak, however interesting they may be.
To my mind, the strongest arguments for authorship by Lazarus - really the only ones worth considering - are that the fourth gospel does single him out as someone loved by Jesus (11:3) and that it's only
after that point that we start hearing of 'the disciple Jesus loved. The strongest argument against authorship by Lazarus is the seeming absurdity of him wandering into the high priest's home after he'd supposedly been plotting to have him killed!
Besides the 2nd century attributions, the strongest argument for authorship by John is the fact that he and his brother James are not directly mentioned in the gospel: Paul and Acts both note the prominence of Peter and John in the early church, and while James died relatively early the synoptic gospels all note those three as Jesus' inner inner circle; it's extremely strange that of the three only Peter is named in the fourth gospel, but if it was written by John, concealing his own identity and omitting his dead brother makes some sense. The strongest argument against Johannine authorship is the high priest's home again; it's not impossible but quite difficult to imagine a Galilean fisherman having that kind of familiarity with the high priest.
From the
internal evidence I'd say that they're pretty much tied as equally likely candidates, but the external evidence tilts the balance heavily in John's favour. Not 'just' the attributions by 2nd century Christians outlined by Goose, though those are really quite impressive compared to the other gospels or even many other ancient works, but there's also at least one other obscure point of interest:
According to Irenaeus (
AH 3.11.1) John wrote his gospel partly in opposition to Cerinthus, and he elsewhere recounts a story told by Polycarp of John rushing out of a bath-house when Cerinthus entered in (3.3.4).
- [Cerinthus] represented Jesus as having not been born of a virgin, but as being the son of Joseph and Mary according to the ordinary course of human generation, while he nevertheless was more righteous, prudent, and wise than other men. Moreover, after his baptism, Christ descended upon him in the form of a dove from the Supreme Ruler, and that then he proclaimed the unknown Father, and performed miracles. But at last Christ departed from Jesus, and that then Jesus suffered and rose again, while Christ remained impassible, inasmuch as he was a spiritual being.
~ Irenaeus, Against Heresies 1.26.1
The fourth gospel doesn't mention Jesus' birth and instead emphasizes his pre-existence; it doesn't mention Jesus' baptism; and it doesn't describe the eucharist ritual. Why would those be missing, particularly the latter two uniquely among the gospels? There are some theories, but one is that it fits with the anti-Cerinthian intent of which Irenaeus wrote, omitting the events which would most likely be associated with the supposed arrival and departure of 'Christ' from Jesus' body. (It's also worth noting that while 1 John 4:2 might be interpreted as an anti-docetic message, it could just as likely be anti-Cerinthian, emphasizing that Jesus
is Christ in the flesh rather than a temporary vessel of a purely spiritual Christ.)
In fact the fourth gospel elsewhere emphasizes the importance of the eucharist ritual far, far more than any of the other gospels - ch6, especially v52 forwards - so short of convoluted appeals to different layers of redaction its absence from the last supper scene really does require some kind of explanation. Imagining that Lazarus wouldn't write about something he wasn't present for (even though that's probably most of the gospel's contents!) really doesn't work at all. But it does seem consistent with the gospel being written in part with an anti-Cerinthian theme, as Irenaeus/Polycarp suggest of the apostle John.