From the very first episode where we got to see future Ben, Ben 10,000 became an extremely popular concept in the fandom, and there was a general desire to have more episodes with him or else have the sequel series transition towards Ben becoming his future self. Each era of the show gave us their own Ben 10,000.
The original Ben 10,000 was one who never took off the original Omnitrix and quite a serious and no-nonsense person who has become a great hero known all around the world. In essence his reputation is exactly what 10 year old Ben would've dreamed of. But he has lost his sense of fun and ability to enjoy life because the duties of being a hero have overwhelmed him, to the point where he doesn't even prioritise seeing and spending time with his family over missions. He has also unlocked Master Control permanently and the timeout feature does not apply to him - again, something that 10 yo Ben would've only dreamed of. Yet he spends too much time in his alien forms and not enough as himself. Of course, by meeting his past self he learns that even heroes deserve the right to enjoy life and hold their family close to their heart. What made this version of Ben 10,000 great is that it is convincing that Ben grows into this version of himself especially looking at how he acts as a 10 year old after he gets the Omnitrix, and he actually has character developement. He also appears in "Ken 10" but he's not really the focus in that episode, mainly trying to be a responsible father to his son Kenny and trying to protect him, despite Kenny wanting to follow in his dads footsteps of being a hero.
Ultimate Alien introduced their own Ben 10,000 who comes from the future to help his younger self defeat the timewalker Eon. This Ben didn't have so much a backstory or his own character arc, mainly because he wasn't the main part of the episode. As it turns out, Ben's future changes every time he meets his future self, resulting in a different Ben 10,000 every time, with this Ben being one who never took off the Ultimatrix. Unfortunately they gave this version of Ben's future a kinda cringey gimmick known as the "Ultimate Ben" form, where he can access all his aliens powers while remaining in human form. This is pretty universally disliked in the fandom even by fans of Ultimate Alien, especially since it takes away from the entire thrill of seeing Ben actually transform into different aliens. This version of Ben's future is kinda underwhelming, and the episodes plot and no real direction in terms of Ben's developement (unlike the original) didn't help, especially since we never actually got to see his future world, his relatives and friends there etc.. I will give Ultimate Ben credit though: I think that his personality is what I envision Ben 10,000s to be like. Sensible, mature, but also retaining a bit of swagger and cockiness from his earlier years
Omniverse continued by introducing their own version of Ben's future (who we'll call Ben 10k). This Ben shares more similarities with original Ben 10,000 in that Kenny is shown again and the future world is similar to what it was. In my opinion, this Ben 10,000 had a slightly generic personality, being your typical dad or older mentor figure depending on who he was with. The idea of the Biomnitrix and this Ben 10k using alien fusions was another unnecessary gimmick which was only marginally less lame than Ultimate Ben, even though the fusions are nicely designed. Surely Ben would be respectful enough to not just ditch the Omnitrix which the greatest mind in the galaxy made for him (specifically for him given that this is the "final" Omnitrix which was made with Ben in mind) just because he wanted fusions. However to Omniverse's credit, there is quite a lot of expansion on this future world especially with regards to the time war episodes, and it's good to see the other future characters and how their relationships have evolved. And the development of his son Kenny and his alternate personality as the timewalker Spanner is pretty neat I must admit.
So all in all, I personally like the original Ben 10,000 the best but all of them have their positives. Now the question is, what is Prime Ben's future supposed to be? Some people believe that he should end up exactly as the original Ben 10,000 because they don't buy the idea of the timeline diverging whenever Ben meets his future. Some people think that Ultimate Ben should've been his future because there's a line where he says that he remembers these events as well as Paradox seemingly confirming this. Some people think that Ben 10k from Omniverse should be the definitive future because he's part of the Maltruant time loop with his younger self.
In my opinion, I think it's fine for Ben's future to change every time he meets his future self. I like the idea that fate is not set in stone and part of Ben's character development is making sure that he does not end up like the original Ben 10,000. But I don't think that gimmicks are necessary at all. Fundamentally Ben 10,000 is an older, wiser version of his child or adolescent self who still wields the Omnitrix (rather than having a gimmick) but has his own set of issues to deal with emotionally as he grows up and has spent so much of his life as a hero.