1. Regis Rohellec Terzieff-Godefroy
Wise and charismatic companion of Geralt and simply the best character from the books. His talk about vampires is legendary.
2. Olgierd von Everec
In my opinion Olgierd is the best character from the games. He is an antagonist who did terrible things, but at the same time he is likeable and if you help him, he seems to become a better man. CDP did such a great job with him - he really looks like a man with the heart of stone. All the characters around him - his Free Company, Vlodimir, Iris and last but not least Master Mirror - they are all perfect. And the boss fight is awesome - I enjoyed the fight itself as well as You're immortal track (which belongs among the best ones in the whole TW series) and the Deluge reference. There are so many details that make him memorable, I am simply overwhelmed.
3. Philippa Eilhart
I love sorceresses and Philippa is a fascinating one. Sometimes ally, sometimes antagonist, she just follows her agenda, fails, but always survives. And I really enjoy her conversations with Geralt. I probably liked her most in TW2 - her megascope talk with triss, lesbomancy and Loc Muinne roam (blinded sorceress killing everything she hears) are just a few examples of moments I will not forget.
4. Sigismund Dijkstra
Both in TW3 and books he is one of the best characters. His dialogues with Geralt are great, but also his mission to Kovir and conversation with Esterad Thyssen in the Lady of the Lake is magnificent. What a pity that he acts like a fool in the end of the Reason of State quest.
5. Gaunter O'Dim
The true devil who uses poorly formulated wishes to ruin people's lives is the best (pure) villain in TW3. And meeting Professor Shakeslock...you just feel how dangerous Gaunter is.
6. Geralt of Rivia
No comment, he is a great protagonist.
7. Letho of Gulet
Before HoS he was for sure the best antagonist of TW series. I really appreciate that I didn't have to kill him and that it made sense story-wise. Vodka?
8. Thaler
When I play TW1, I always look forward to Vizima Confidential quest and meeting Thaler.
9. Azar Javed
He is intimidating and has great quotes (though they are not original as he only repeats what Vilgefortz said). Anyway, in my opinion he is a good antagonist and I replayed his key scenes many times. If only I could say the same about Eredin.
10. The best character from Blood and Wine
I need at least one spot for the best character from the upcoming expansion as CDP promised a memorable and charismatic villain. I am looking forward to it!
Honorable mentions: Leo Bonhart, Rience, Eskel, Lambert, Triss, Yennefer, Zoltan Chivay, Field Marshal Duda, Borch Three Jackdaws, Dandelion, Vernon Roche, Iorveth, Siegfried of Denesle, Vincent Meiss, Jethro, Kalkstein, Lytta Neyd, Dethmold of Ban Ard, all the other sorceresses and mages,...