I genuinely think VF4 Pai was her best and most aggressive/mature iteration
Virtua Fighter 4 is where I think Pai peaked as a character. Her voice sounds way more mature than in VF5, she looks overall more serious and her design is just top notch. Along with both of her themes which totally fit here imo (Blue Impact and Without Hesitation). Both of them are absolutely beautiful. Not that I dislike her design or themes in VF5 (which I also like), but it sort of feels like a step down when compared to VF4.
Plus it has my favorite costume of hers. That helps as well