I agree that Sanji's opponents are usually more extravagant and over the top personality wise, but looking baddass and competent are two completely different things.
Zoro vs Kaku runs around Kaku's Devil Fruit being goofy (despite being strong), while Sanji vs Kaku runs mostly around Robin. Jabra's personality also gets more highlighted during the fight, compared to Kaku's against Zoro, who doesn't.
So its literally all about the difference between their personalities, since i could easily argue Aramaki has the best feats an Admiral has ever got in the series, with the exception of Akainu and maaaaaybe Aokiji.
Aramaki clearly has a Black Blade too, so its something to keep in mind... I think there are good argues for both Sanji vs Kizaru or Ryokugyu and Zoro vs Kizaru or Ryokugyu, and lets not forget Fujitora
Zoro vs Kaku runs around Kaku's Devil Fruit being goofy (despite being strong), while Sanji vs Kaku runs mostly around Robin. Jabra's personality also gets more highlighted during the fight, compared to Kaku's against Zoro, who doesn't.
So its literally all about the difference between their personalities, since i could easily argue Aramaki has the best feats an Admiral has ever got in the series, with the exception of Akainu and maaaaaybe Aokiji.
Aramaki clearly has a Black Blade too, so its something to keep in mind... I think there are good argues for both Sanji vs Kizaru or Ryokugyu and Zoro vs Kizaru or Ryokugyu, and lets not forget Fujitora

I think we will have:
Luffy vs Akainu
Sabo vs Fujitora
Zoro vs Kizaru
Cook vs Ryokugyu