Obi Wan. Fenix doesn't have the power to toss his opponent across the room using his powers. Obi Wan was able to fend off 4 Light Sabers, so I think he can handle 2 Psi Blades
Fenix, because of a couple things. A, no one specified him as a Zealot. It's hard to argue with a BALL OF FLESH MELTING PLASMA. Yeah, Obi-Wan's got a lightsaber, but that can only do so much, ie he can't deflect a starship's blaster fire, so chances are the photon cannon is a bit too large. B, Fenix and Tassadar were hella tight. And Tassadar, before he died, was one of the most insanely powerful beings in the universe at the time.
Fenix would win. All Protoss have some psionic talent, and seeing as Fenix was a badass, I wouldn't be surprised if he was looking into Obi-Wan's mind for most of the battle. Also, which Obi-Wan are we talking about: pre/during the Clone Wars or post Clone Wars?
Still Fenix. Also, Fenix has two blades, massive physical stature, and psionically AND mechanically enhanced reaction time and strength.
Fenix couldn't beat kerrigan, who fights with claws, how exactly would he beat someone using a Lightsaber?
Fenix was merely a Praetor. Kerrigan was a held in high regard commander of the Zerg until she became the Queen of the Zerg.
I think I got to give the edge to Fenix but only in Zealot form. The attack from a Dragoon would be to easy for a jedi to dodge and once Kenobi got close he would cut the Dragoon to ribbons. As for the Fenix (Zealot) v. Kenobi I would say Fenix has enough psionic ability to atleast counteract whatever Kenobi would try and Fenix should win handily in a blade battle because of his equipment and training.
Kenobi. Despite Fenix's mechanical and psionic enhancements, The Force just can't be beaten by a mere Zealot OR Dragoon. Kenobi also has massive experience with fighting against multiple blades, in both battles with Darth Maul and General Grievous. His experience with the Acklay that attacked him in the Petranaki Arena during Star Wars Episode II: Attack of the Clones would be quite similar to Dragoon fighting, minus the Dragoon's ranged attack, which, as was pointed out earlier, would be quite easy for a Jedi to dodge.
A 'mere' zealot? You do realize of course, that though Obi-Wan is a Jedi Master and has had years of training, Fenix has had roughly three human lifespans of training and battle experience? Saying a 'mere' zealot is saying a 'mere' Panzer tank brigade.