I've only seen First Class and Logan fully, as well as The Last Stand a long time ago, though I know enough about the other films to offer some thoughts on them.
The first film is pretty mediocre with it just being about a mutant turning people into mutants, but is at least somewhat faithful to the comics' theme of humanity's conflict with the idea of Mutants. The second film is slightly worse due to just being mutants vs mutants without any other driving force. Both 5/10.
The Last Stand is shit, both as an adaptation and its own film. What was a space opera that was an entertaining Star Wars homage turned into just a cameo cycle of mutants that only remembers it has a plot in the last 20 minutes. 2/10
X-Men Origins: Wolverine is a prequel focusing purely on such a terrible gimmick as amnesia and betrays the idea of Deadpool by turning him into everything he isn't. Pretty telling that this was written by one of the two directors behind the bottom of the barrel in writing quality that is Game of Thrones Season 8. 1/10.
First Class is decent as an origin story for the X-Men with decent character chemistry, training progression and it's good to see the mutants interact with their environment through conflict with humans. Other than that though, it requires on some major plot conveniences and some dumb character decisions at times, though only by enough to make it fine rather than good. 6/10.
Days of Future Past and X-Men: The Wolverine are essentially the same film - both featuring terrible writing contrivances (time resets and general lack of logic respectively), yet both work well as dumb action films that act as tributes to the campy yet cool style of 80s films (Terminator and most 80s action flicks respectively). 5-5.5/10
Apocalypse is essentially a worse version of The Last Stand - butchering an adaptation of a classic story arc to instead become a fanservice series of cameos to have mutant vs mutant battles and a generic god-complex villain. 1.5/10.
Finally, there's Logan, which is without a doubt the best of the franchise and the only one I'd give a solid recommendation to watch. Along with being the most easily digestible outside of First Class if lacking in-depth knowledge of the franchise due to the idea of the other X-Men stories being stories within the story that were embellished, it does a great job at showing the degradation of Logan and Xavier in a coherent and sympathetic way (extra commendable when coming out in the same year as the abortion of a film that attempted the same called The Last Jedi), it does subversion well through the former as well as making it apparent the bleak world can't be fixed and makes the themes of hope and redemption within it both more impacting in this down-to-earth superhero film and for the internal resolve of the characters through striving for it. It also has the more superficial quality of being the first X-Men film to present Wolverine as violent as his combat should be and the acting from both Hugh Jackman and Patrick Stewart is great. The only real flaws I'd consider with it would be that the main villain is pretty generic and somewhat dampens the internal conflict of Logan by making it external as well as the references to the western within it being too overt, though beyond those minor complaints it is still the best superhero film since Watchmen (or the third best superhero film overall, #1 being Watchmen and #2 The Dark Knight). 8/10.
In summary, Logan >>>> First Class >/>> The Wolverine > Days of Future Past > X-Men > X-Men 2 >>> The Last Stand > Apocalypse > Origins: Wolverine