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The FW stats are fluff-based, so they are quite accurate.

Anyways, in terms of pure 1vs1 combat prowess here are my ideas.
Top Rank:
1. Angron (As a gladiator turned bloodthirsty berserker, fighting is all Angron has ever done. He also defeated Leman Russ in 1vs1 combat. The fact that he is called 'The Red Angel' tells you all you need to know about him.)
2. Perturabo (The Lord of Iron is pretty much a living mountain. He also smashed Fulgrim into a pulp despite the latter's trickery. The fact that Perturabo is completely confident in going after and fighting Fulgrim at the height of his power and the fact that he defeated him without any deamonic aid of his own is what gets Perturabo this spot.)
3. Fulgrim (Renowned as a great fighter and duelist, a reputation he lived up to by defeating 2 other Primarchs, which is a feat no other Primarch can boast of. Even without the aid of Chaos, he still remains incredibly skilled and powerful)
4. Leman Russ (The Wolf King snapped Magnus' spine over his knee and could stand up to Angron quite well)
5. Lion el'Jonson (Famed as a great swordsman, defeated Curze and was capable of matching Leman Russ in a brawl)

Medium rank:
6. Sanguinius (He may look like a pretty boy, but he was known as a great fighter and eats greater daemons of Khorne for breakfast. Apart from that he does not have many feats however and he was completely unable to stand up to Horus even a little bit, which is why I rank him lower than most rank him.)
7. Horus (Lupercal was known for his great prowess in personal combat, but most of his feats were accomplished with the aid of the Chaos gods, so it is hard to judge him properly. After his fall to Chaos he certainly becomes #1, killing Sanguinius without much effort and he would have even gotten away with slaying the Emperor if it had not been for that one meddling Guardsman)
8. Guilliman (Noted as a capable fighter and held his own against Angron and Lorgar.)
9. Jaghatai Khan and Mortarion (These 2 have little in the way of feats, and were completely matched with each other, which is why they get to share a spot in the middle)
10. Ferrus Manus. (He lost his head in the fight with Fulgrim but seemed to be quite a solid fighter)
11. Vulkan (overpowered Curze even after being tortured)

Low rank.
12. Corax (Difficult one. Had trouble against Lorgar, and does not have many feats apart from that. Relies probably on hit and run tactics more than fair fights)
13. Magnus. (A great and powerful psyker, but that did not help him much when he had to face Russ in personal combat. Personal combat probably is not something that Magnus has spent much time training for.)
14. Curze (The Night Haunter fought a lot against other Primarchs, and generally holds his own quite well. He does virtually always get beaten in a fair fight though, which is why he is ranked so low. He is probably more of a murderer than a real fighter.)
15. Alpharius (Would have killed Dorn if the 1vs1 would have remained a 1vs1. Apart from that he is mostly a strategist and seems to be one of the physically weaker Primarchs)
16. Dorn (A strategist and tactician rather than a fighter. Lacks any impressive achievements and nearly got killed by Alpharius)
17. Lorgar (Lorgar was a preacher, he preferred fighting with words rather than weapons. He seems to be regarded as the physically weakest Primarch. After his fall to Chaos he did become a very powerful psyker though.)