Definitely Philippa! Best boss ever! And her character is not that black and white. She is not a 100% antagonist and thats what makes her character really interesting.
The same holds for Emhyr and Dijkstra - all of them are anti-villains. Only Radovid is EVIL.
I chose Philippa too, mainly because I have a love-hate relationship with sorceresses like Philippa or Sheala de Tancarville - they simply fascinate me. Philippa is such a manipulative, arrogant and egoist bitch who always survives and pursues greater good in her own twisted way. It is fascinating how patronising she is given how many times she failed to achieve her goals. If other characters make a fatal mistake, they die. But Philippa? No.
She is just unique.
Emhyr is better Tywin. Dijkstra can be compared to Varys (both are not interested in personal gain, they are just patriots who want to make living in their realms better and are ready to do whatever to achieve it). Radovid is just a very ruthless and capable ruler who went insane (so many of them).
But who is similar to Philippa?
One more thing, I like Philippa's voice and condescending behavior when she speaks to Geralt.