Eh my personal head canon.
Well I would like it having been: Fallout 1. Fallout 2. Black Isle's Fallout 3 but unfortunate the last one was never made and several of its ideas were used for FNV instead.
So my head canon is: Fallout 1, Fallout 2. Fallout New Vegas.
Now I don't hate Fallout Tactics as I enjoyed it a lot when I played it years ago and I do like the idea of the Calculator and its army of robots, another pre war relic causing mayhem and destruction. But I am not sure about Vault 0's concept as some of it kind of sounds what the Enclave oil rig was (a hideout of politicians, heads of industry, and other important figures and their families) though I guess it could be retconned as being the shelter for lower ranking/non Enclave politicians, influential people from the private sector, movie stars and so on (though they would probably take shelter in Vaults closer to where they lived and worked).
I do think however that Cheyenne Mountain would be wiped of the map by the Chinese as suggested in Black Isle's Fallout 3 so the Calculator and its robots should have been somewhere else.
Also, I do not hate the Midwest BOS faction and I could even see them still exist in the FO1/FO2/FNV timeline but I really don't want to make them such a powerhouse as they would end up in any of the Tactics' endings.
They would be more powerful than their West Coast counterparts (I don't care for FO3 and FO4 so Lyons/Maxon's BOS does not exist) because of their open recruitment policy but they are slowly developing into this technology obsessed militaristic fascist organization, seeing themselves as the rightful heirs of the former US.
Now regarding Fan Mods and Total Conversions.
In general I do not care for Fallout of Nevada so I consider it and its contents non canon.
I like Fallout Resurrection and if Black Isle's Fallout 3 is non canon the places, people, and events of this game don't clash in general with the FO1, FO2, and FNV, though one of the differences would be that the Hub of course was never destroyed by Super Mutants so the traders of Little Hub are simply migrants from the West.
Hmm what I am thinking a lot about is something someone here has also been discussing, that Ghouls were originally just unique to Necropolis before they migrated to Gecko and other places.
I never minded the idea that there were more Ghoul populations in the wasteland such as the suggested Reservation in Black Isle's Fallout 3 (I so much want this place to be appear in a Fallout game) but I really dislike the idea of there being thousands of zombie Ghouls after the war and that people can easily change into Ghouls.
Now I have not played Fallout Sonora yet but I know a lot about its storyline from reading various spoilers.
There are elements in it that I like as with Fallout Tactics and Fallout Resurrection in general but there are also elements that I feel clash I am going to consider this game non canon.
Hmm, thinking about this all again makes me wish I could have a FNV expansion mod or TC made that would be set in New Mexico and would involve the Reservation/Children of the Wasteland, the Legion (spreading Eastwards), and the (Vault) Empire from Fallout Resurrection. (no despite their name they are not an expansionist empire)
And then there is of course my own Fallout Texas which I would like to make/see being made.
Now this game does have Ghouls in it but I could easily remove them if I go with the idea that the only source of Ghouls was the Vault in Necropolis.
I would like to leave in Super Mutant migrants from the West though.
Perhaps some new kind of human mutant that has become more animal in behavior and eats human meat.