It all depends on how a reboot is being done. Usually, I'm also a bit against reboots, but if the reason why a reboot is needed, such as the content of the original work wouldn't hold up too well in current times or the original characters were too flat in their personalities, then I could see a reboot being a huge benefit for the characters and the franchise, if it's done right.
Definitely the 80s with the years 2000-2007 close behind. The 80s really defined the X-Men as the characters they are known as today and they had many great stories such as "The Dark Phoenix Saga," "God Loves Man Kills," and "Days of Future Past" that are still looked at fondly to this very day. The years between 2000-2007 was also a great time for the X-Men as many have pointed out, it helped transitioned the X-Men from being students at Xavier's School to actually teaching a new generation of mutants to defend mutantkind, which was something I really enjoyed and I wished that Marvel actually tried to utilize the new X-Men students a lot more.
I honestly don't think that Marvel will ever end their X-Men comics since they are a huge part of the Marvel universe, but I can see the X-Men getting less popular over the years, especially if Marvel doesn't get the rights back to the X-Men movies soon. I say if the X-Men starts losing their popularity it would be on either one or two things: if superhero movies start losing their popularity, meaning that the X-Men will lose their popularity as a superhero franchise or if Fox refuses to give up the rights to the X-Men movies, which I don't see Fox giving up the X-Men anytime soon since they already have many plans for future movies.
@arturocalakayvee: I agree with all this. Having the X-Men in the MCU would have made things even more confusing, especially whenever they have to explain about how come the X-Men are mistreated but not other superheroes who have powers and are not mutants.
I honestly don't know myself because while I want X-Men to be back at Marvel, I know that because Marvel already got too any superheroes in their universe, that putting in the X-Men might cause even more confusion in the MCU.