The following are the most skilled fighters, in terms of overall fighting ability.

As to the "who would win" in a tournament where only fighting skill and weapons are permitted...
 

Top tier fighters

Second tier fighters

Renshi's ability to learn his opponent's fighting skill would not be nullified in a Pan Stellar, because this ability is innate. It is not a skill he has control over. Regardless, since Renshi has already learned what he needs to defeat Q'Aestor, he would be in first place. However, his skill learning ability does not work on most alien species, so it may not work on Challenger or Ravager.

Q'Aestor has a fair chance of winning against Meridian. His strength may not necessarily match hers, but he has a millennium of fighting experience, as well as, many appendages. Whether he actually would defeat her is still debatable, as Meridian is quite formidable.

Meridian could potentially take first place, but she has always lost to Renshi. She would, however, easily defeat everyone else, even Challenger would be no match for her.

Challenger would easily defeat Farpoint and Ravager.

Farpoint would defeat Ravager, even with Ravager in his enhanced form, Farpoint being a better fighter.

Ravager would likely win against Silverlance. His strength and fighting ability is higher, but Silverlance silver exterior would protect him from Ravager's blows. However, Ravager does not need to knock him out. He only needs to immobilize him, and win by default.

Dark Slayer is the best fighter on Earth, but could not win against opponents 20 plus times her strength. She would defeat every second tier fighter, however. Ironically, she would stand a reasonable chance against Renshi.

Mantis has the potential to beat Dark Slayer, but the strength difference would be her greatest obstacle. She would very likely defeat Jihad, as for Sumo Juggernaut, without the use of his Shiko, he would be a regular Sumo wrestler and no match for her or even Jihad.