Well, Obi-Wan's only chance would be in a straight duel, as in the three marksman starting out within range of vision. If Atton has time to set up his Jedi-killing traps and formulate a plan, Jango Fett and Han will take out the gassed and hurt Jedi.
Even in a straight fight, I can see Obi-Wan getting shot to pieces. Against Han Solo, who stood up to a squadron of stormtroopers and has a blaster modified to the point where it leaves craters in cantina walls, a Jedi-killer of notoriety and Force-sensitivity, and the "deadliest man alive", I'm not sure that Obi-Wan can triumph. And if he does, it'll be by him taking an ObiLuck before the battle and pulling one of his astounding survival feats.
All said and done, I'm going with the trio on this one.
I like Kenobi, but its a long shot for him to win this. I mean he didn't fare to well against Jango alone. (although he did get short by the Slave1 and by that annoying fett kid, whats thats kids name again.. lol 😛)
Anyways, If somehow he could separate these people then he might win. He'd beat Han easily. I just think that with Fett and 2 other people, its too much for him to avoid being hit, even if hes a master of form III.
We also are not accounting for Obi-Wan's luck. Kenobi's gotta be the most lucky Jedi ever.
which is why his ANH "In my experience there's no such thing as luck" line makes me laugh. lol
Anyways...there is also one thing I didnt account for, Obi's saber skill in Eps. III pwnes his saber skill in Eps II. By ROTS I actually think Kenobi's prolly good enough to block and deflect the blaster bolts back at these 3 people. If any Jedi timed it right he/ she could deflect the bolts back at any blaster wielder and kill/ really hurt them, and Kenobi is THE master of saber defense in the order.
Now that I think about it, I think Obi would drop Han and Atton pretty quickly, especially Han, then it would be him vs. Fett. Now Fett is good, but Obi in Eps. III is pretty badass, if he could get rid of Jango's jetpack somehow then I think it would be like "Mace WTFpwnes Jango" moment in AOTC.
And even still, Obi's luck might just make a return. Say something like this:
*Obi jumps so that the 3 dont surround him*
*Han fires and Obi deflects the bolt back at Atton and hurts him bad*
*Obi runs at Han and Jango deflecting their bolts. As he gets close, Jango flies away with his jetpack leaving Han alone on the ground*
*Obi then force pushes Han and stabs him in the eye, killing him, then swings around and cuts of Atton's head while he is in pain on the ground*
*by this point Jango has had enough time to line up a shot and while Kenobi is distracted killing the other 2, Jango prepares to fire his jetpack rocket, a killing strike that would for sure end Obi's life. But all the sudden, the rocket ignites but does not launch out. His jetpack malfunctions as a result and Jango flies into a wall and explodes without Obi even knowing*
Something like that kinda Obi-like luck...lol
ROTS Obi Wan is going down..
Atton is a Jedi Killer, Jango is a Jedi Killer, Han is Han.
Now the rate of fire in these weapons are going to be to much for him to handle. And these guys aren't stuipd enough to just stand there and shoot without jumping to the side if blaster bolts come back. I just don't see Obi Wan pulling this off, unless he's gassed.
In a straight out gun fight I give this to Obi-Wan. Reason: Soresu is known for it's advantage over blaster fire.
Atton is Jedi killer, true, but he relies to much on poisons/gassing/secrecy. In a straight out gun fight he doesn't have that advatnage. Jango could fly away and blast from afar, but Soresu nullifies that advantage. Han Solo, IMO would be the first to fall. Then the other two.