No one's good.
They're all ambigous. It depends on what point in life we look at Kitty and Nat.
Kitty:
Betrayed her government
Stole
Robbed Graves
Possible assitance in killing
Lied
Nat:
Betrayed Kitty
Broke promises
Went behind both his masters' backs
Lied
Sought revenge
But.....
Kitty:
Saved Nat's life on several occasions
Worked to help commoners achieve liberties
Saved Jakob (Or tried)
Defended London against demons
Brought djinni/humans together
Nat:
Brough Lovelace to justice
Saved hundreds of lives
Saved Kitty from Makepeace
Kept his promise to Kavka
Went back for Ms. Underwood
Defended London against demons
Sacerficed his life
See? People aren't good nor are they bad. It's their choices who make them who they are. In the end, both Nat and Kitty can be thought of as honorable.
"You belong in Gryffindor,
where dwell the brave at heart,
Their daring, nerve and chivalry
set Gryffindors apart."