I'll go with Ostapenko at the Baltic Open. She didn't wear it a lot because of her awful form. However not only did it look awesome, but also represented the colours of Latvia in a great way. The model also helped of course.
1. Osaka's USO and PPO look - even the one with white;
2. Adidas Wimbledon look and the one hit wonder for Osaka;
3. Yonex throughout the year for Yastremska and Nastja;
4. Fila Kiki's outfit at YEC and Zhuhai.
OK I have to confess that I have a bit of a Bjorn Borg bias —still the coolest player of all time, bar none— so I'm generally happy to see his iconic pinstripes all over the elite girls in 2019, on Kiki Bertens, and Barty the champ in her baseball/bomberjack. But above all else it is Pliskova who looks the best in Borg's pins. The outfit and its legacy finally found a player that fits it the most in terms of character and appearance: from her ice maiden face, to her height, to her penetrating game.
1. Maria Sharapova US Open
2. Naomi Osaka Wimbledon
3. Maria Sharapova RG dress (Mallorca)
4. Naomi Osaka US Open (white and black version)
5. Venus Williams Miami
6. Serena Williams Wimbledon
7. Venus Williams Australian Open
8. Venus Williams Indian Wells
9. Amanda Anisimova RG
10. Garbine Mugaruza Wimbledon