[X] Woman
If a traitor primarch is chosen, I think it'd be rather helpful to not share the exact face of some of the most reviled people in the Imperium given its galaxy spanning nature. Myth for most, admittedly. But the likes of the Inquisition will know. Putting that aside, it could be helpful having something about the PC that would separate them from the chosen primarch---something that could keep them anchored, remind them that they're their own person. Given the primarchs nature as a brotherhood, adding a sister to that seems a good a anchorpoint as any.
[X] The Phoenician (Canon)
Fulgrim is genuinely one of my favorite primarchs. I just can't not vote for him.
[X] The Lord of the Red Sands
If there was ever a choice pick in the interests in ensuring the clone will be their own person, this would be it. The real Angron never got a chance to live beyond the Butchers Nails. Besides some tortured memories, this is essentially a blank slate.
[X] The Great Angel
For the most part I'm neutral on Sanguinus, even leaning towards dislike sometimes. But in this scenario? Well, theres definitely some potential for interesting developments.