Gotta break it down. If we are talking raw potential with the Force, then Anakin or Luke wins, hands down. Rey (too little information available) might sneak in there too.
If we're talking martial prowess we should compare the combatants at their finest. Of course an aged Obi-Wan isn't as agile as say 30 yr old Obi-Wan.
Since OP asked for a Galactic Republic Obi-Wan I'll not include Luke in this ranking list. Also, too little material available to compare combatants from different eras with each other. There are some great VS series on YouTube for those who want to see some proper breakdowns of these characters!
http://images5.fanpop.com/image/photos/29400000/Anakin-clone-wars-anakin-skywalker-29478824-1280-720.jpg
1) Anakin (Jedi) peaked at the time when he defeated Dooku, alone. In a pure lightsaber duel. This is an absolutely amazing achievement, but I suspect many don't realize exactly how big it is until you've read up a little on Dooku.
http://static3.businessinsider.com/image/55798f726bb3f7f87149d052-480/christopher-lee-count-dooku.jpg
2) Dooku (Sith) Dooku probably peaked during Clone Wars, where he was absolutely unstoppable. Took on Anakin+Obi-Wan several times, survived Ventress' ambushes twice. Manhandled Obi-Wan with his Force pushes and in duels. Called the finest Jedi of them all by Yoda. One of only two Jedi (the other being Yoda) who defeated Windu in a duel (source: New Essential guide to Characters. Not canon anymore but it's still a source of info on how they gauged the character).
https://i.ytimg.com/vi/aKXz5Daczog/maxresdefault.jpg
3) Mace Windu, peaked during his battle with Sidious. Let it be noted that Mace believed his old Padawan Depa Billaba to be his superior with the blade. But Mace had Shatterpoint, his ridiculous Force augmentation and finally his deep commitment to Vaapad made him almost invincible in a duel. Especially vs Dark Side foes.
http://screenrant.com/wp-content/uploads/star-wars-obi-wan-kenobi-movie.jpg
4) Obi-Wan (ep 3) after the defeat against Dooku in episode 2, Obi-Wan intensified his Soresu training. This shows in the Clone Wars, where he single handedly defeats Maul AND Savage Oppress. Obi-Wan is tough to gauge. We only know that he can take absolutely insane amounts of punishment. He has yet to be defeated in a pure lightsaber duel, but he's prone to having his Force shield penetrated.
His strongest offensive trait is his tactical sensibility. Mid battle against Grievous he changes the angle of his parries, cutting off the droid general's limbs. His win against Vader on Mustafar was due to his ability to make tactical decisions on the fly. He survived against Maul and Savage by repeatedly kicking Savage in the knee(!).
(Yoda) not included on this list because of... Reasons. He's probably up at the top, even though his performance in any of the present canon material doesn't really support it.
Important point: Any of these characters could probably win a battle against any of the others, in the right circumstances. It's extremely hard to gauge their relative strengths and weaknesses. Dooku was overwhelmed by Anakin's offense, but Obi-Wan likely wouldn't. Mace would likely defeat Dooku since he went to the Dark Side, but that is likely more due to Mace's combat specialisation. He would likely beat Anakin too, due to sheer experience. But looking at the Clone Wars, Anakin performs the greatest feats and pulls off what others thought impossible.