What is Louka's personality like, and what is the basic difference between Bluntschli and Sergius?

In George Bernard Shaw’s play, Louka is a clever, manipulative, resourceful woman who works as a servant in the Petkoff household. Louka is engaged to another servant, Nikola, but she obviously has her sights set elsewhere as she resents being expected to adopt a deferential attitude. Nikola seems content with his situation but also has aspirations to own his a store someday.
Sergius Saranoff is a military officer engaged to Raina Petkoff. A dashing figure, he fancies himself a brave warrior. When he appears in their home following a battle, he has been declared a hero, but that turns out to have been an error. Furthermore, he reveals his disloyalty to Raina by making advances to Louka. Finally, they are matched as a couple.
Captain Bluntschli is a mercenary who considers himself a pragmatist—that is, while he fights for pay rather than nationalism, as he is Swiss. His pragmatism extends to seeing heroism as having limited value, and as the play opens he is hiding from the war rather than participating in a battle. Whether Bluntschl is actually a coward or just exercising common sense is a question raised throughout the play. His combined intelligence and experience have given him strategic skills useful in battle, but he can only utilize them if he can remain detached from concern over the results. Ultimately, his character is revealed as far braver than Saranoff’s, and he and Raina end up as a couple.

Louka is Raina's servant. She resents being a servant. She is engaged to another servant, Nicola, who is happy with his position.
Louka shows herself to be a person capable of deception. She allows Sergius to court her, kiss her, and embrace her behind Nicola's and Raina's backs (Sergius is engaged to Raina).
The basic difference between Bluntschli and Sergius is that Bluntschi, as his name implies, is bluntly open and honest. Sergius, on the other hand, is deceptive. He pretends to be the dashing military hero even though he knows he only won his battle because the other side's leadership was even more incompetent than he was. He pretends to be in love with Raina because she is a person of his social class, and it is expected that they marry. He sees life as playing roles, while Bluntschli tells it like it is.