Every Primarchs have some flaws, some more, some less. For my personal taste, Russ is the best primarch.
Guilliman, the whole tactical thing and Roman theme appeal to me. Notable mentions Curze for his personal beliefs Sanguinius for just being amazing, also black rage and red thirst Pre Heresy Horus Angron.
Perturabo the master of offensive siege warfare Fought because of he knew his father would never for give him Granted daemonhood of the last of his brothers Fought his rival Legion the Imperial Fist into almost decay Broke Dorns Willpower Never ran for the from a horrific battle Best term of personality Klingon Doesn't fight because he doesn't want too unless he wants action like in the 10th black crusade Has his own Fortress Planet Planet Killer
My favorite is Russ but I have to admit I believe Sanguinius to be the best primarch. Other than mutations he has it all. Strength, psychic ability, martial skills, determination, etc. You can go on forever. He also willingly walked into his death knowing it would help the Emperor.
He also died before could make many mistakes. Many of the primarchs had their worst moments after the Horus Heresy. Sanguinius went out in a blaze of glory and never got the chance to have one of those moments.
Lorgar is the most human of the primarchs and he got shot twice by a plasma blastgun. but the strongest would be Angron he harnessed his anger and uses it as a weapon. just my opinion.
