We now know an Obi-Wan Kenobi Anthology movie is likely coming. We know absolutely nothing about the plot at this point, and for good reason: not a single word of the script has been written yet. Any speculation about the plot would just be a "shot in the dahk". But there is one area about which we can have a reasonable debate: the identity of the antagonist.
Local Bad Guy
Shane.
Tatooine evokes obvious western parallels. The concept of Kenobi playing a Clint Eastwood-type savior to a small town being victimized by the Star Wars version of a greedy railroad tycoon, a gang of highwaymen, or a classic guy in a black hat is certainly appealing to us.
We would absolutely love this storyline. LOVE IT. But as you may have heard, we're old. As such we don't have a lot of faith in Disney pinning the success of a tent pole movie on a plot that works best for middle aged men who are nostalgic for the westerns of their youth. Disney could create a completely new character to challenge Obi-Wan, but such a character with the wit and skill to take on a Jedi and who was previously unknown to audiences might be challenging. We have a strong feeling that Disney will want to market the antagonist of this film as much as the hero. One existing character that may fit this mold is Cad Bane, possibly a compromise that could bring a fairly popular animated baddie into a storyline that might appeal to us aging folk.
Darth Maul
Obi-Wan already crossed him off his "People to Kill" list. Twice.
Like it or not, Maul survived his bisection at the hands of Kenobi in Theed palace. The Clone Wars made this canon. Big whoop, wanna fight about it? It happened. Move on. Maul is essentially Kenobi's arch nemesis, even more so than Vader, who hasn't felt his presence since... The Duel of the Fates was arguably the best part of the entire PT, and having Maul return to the big screen for another showdown with Obi-Wan should be epic.
Unfortunately, this option may be dead on arrival. One huge positive about using Maul is that Lucas clearly took too far the Seinfeld "leave them wanting more" concept. In general, fans want more Maul. Unfortunately (or fortunately depending on your perspective), this can't happen. The foolish Rebels animated series is canon, and Filoni has already chewed this turf. Kenobi dusted Maul once and for all in the "Twin Suns" episode. It would seem highly unlikely that this showdown would be simply recreated for a film, when it was already hashed out. The only possibility would be if the film depicted a non-deadly showdown and were to take place earlier in the timeline than the Rebels final duel, but that would be a mighty unsatisfying climax for audiences.
Boba Fett
He wants his own film, dammit!
Here's another opportunity for a fan-favorite character to kick some buttocks on the big screen. It would be believable that he could take on a Jedi in a test of wits, or in combat. Perhaps some kind of cat and mouse game on Tatooine in which each tries to outsmart the other in tense confrontation.
Since we absolutely know that Vader cannot be used as the antagonist in this film without creating a universe-shattering continuity problem, there is literally no more marketable villain during the Tatooine years than Boba Fett. Kenobi going toe to toe with Fett would certainly have easy fan appeal. Especially since Fett, like Maul, is still under-realized on the big screen. This would also give Disney a chance to get Fett into an anthology film without having to crack the "how do we make a villain the hero of his own story" nut. But there are huge continuity problems with using Fett as well. In fact, even a mere cameo by Fett could present problems depending on how it's handled. If it becomes canon that Fett knows Kenobi is on Tatooine, why would he not dime him out to the Empire for the reward? Also here, a satisfying victory for Obi-Wan might be difficult to achieve because we know Fett survives.
Jabba the Hutt
He's been practicing his moves.
The Star Wars mafioso is probably the closest we'll get to an evil western movie industrialist in this universe. So long as Jabba only employs his standard henchman in his evil plot, and not any of those preeminent bounty hunters from the bridge of the Executor, the story can credibly steer clear of continuity issues. It would allow Jabba do be a mastermind, without needing to actually fight Obi-Wan himself in what would be another example of a non-decisive and unsatisfying showdown.
We have to imagine that Disney is absolutely chomping at the bit to revisit Jabba's palace on the big screen, and it would probably make Hasbro happy, too. It's fairly well established that the Hutts and the organized governments of the Star Wars galaxy operate in mutual exclusivity, so this could be a sandbox to give Kenobi an adventure, while not popping up on the Empire's scanners. Yes, we know Jabba had an alliance with Empire that allowed him to continue his criminal activities, but unlike the bounty hunters for hire, he would never tip the Empire off to Kenobi's presence. The last thing a crime boss would want is the Empire turning his planet upside down in a Jedi hunt.
So, obviously all of this is assuming this will be a middle-aged Kenobi story. If Disney decides the story will actually be Kenobi: The Teen Years, then: