Not very different. The differences really are minor, and indicate each author's writing style--not different elements. I've done a study on this, and have looked at each element in each of the synoptic Gospels. They all say the same things using slightly different words, and sometimes the same exact words. Some include elements that others don't. But the elements that exist from one account to another are not divided by the use of different words. It was viewed as perfectly legitimate to quote Jesus in slight variations, as in a paraphrase.
For example consider the 3 versions of the Abomination of Desolation. Luke does not use that term, although Matthew and Mark do.
Matt 24.15 “So when you see standing in the holy place ‘the abomination that causes desolation,’ spoken of through the prophet Daniel—let the reader understand— 16 then let those who are in Judea flee to the mountains."
Mark 13.14 “When you see ‘the abomination that causes desolation’ standing where it does not belong—let the reader understand—then let those who are in Judea flee to the mountains."
Luke 21.20 “When you see Jerusalem being surrounded by armies, you will know that its desolation is near. 21 Then let those who are in Judea flee to the mountains."
Mention of the apostles being persecuted and their need to stand firm precedes the AoD or Jerusalem being surrounded by armies in all 3 accounts. And in all 3 versions they are followed by the need for the Christians to flee to the mountains. In other words, the AoD and the surrounding of Jerusalem by Roman armies are the *same thing!*
While it's possible, and maybe even likely, that Jesus repeated the elements of the Olivet Discourse at different times and in different places in his ministry, the Olivet Discourse itself had a specified time and setting, which was immediately after Jesus left the temple and took his disciples with him up on the Mt. of Olives. It was a time for explaining what he had said about the destruction of the temple. Matt 24, Mark 13, and Luke 21 are all versions of the same discourse, the Olivet Discourse.
Using different words, from one author to another, was not viewed as a critical construction, in which Jesus is quoted exactly. Paraphrases were in play to some degree. Jesus may have used more words to explain something, and one author may include a different set of words that depict the same element given in all 3 accounts.
Such is the case in Luk 21 where Luke records that Jesus specifically said Jerusalem would be surrounded by Roman armies. That literally happened. Jesus did not just say there would be an Abomination of Desolation, although Matthew and Mark did record that part of the speech.
It is therefore highly likely that since all 3 versions were couched between the markers mentioned above, that Luke recorded one element that Matthew and Mark did not record, and that Matthew and Mark recorded words that Luke did not record. Since nobody in the Early Church had a problem with this, we must assume that they all understood Jesus to be describing the same event.
If we put all 3 synoptic gospels together, we have a more complete picture of what the AoD was, namely the surrounding of Jerusalem by abominable pagan forces set to desolate the temple and the city. Just how I see it, and apparently how the Church Fathers saw it.
Unfortunately, today modern prophetic futurism wishes to render some historically-fulfilled prophecies still about the future. And I think that's wrong. Certainly, some of the Olivet Discourse included prophecies of the future. But I think the AoD was something fulfilled in 70 AD and in 135 AD.
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