When given something good to do: 10
Episodes such as "Loud as a Whisper" and "The Ensigns of Command" really do much to bring her character out and it's far more than the usual broken LP of
Captain, you can already tell and so can the audience but my job as an actor is not to break the fourth wall, as everyone already knows this isn't a cheap parody or otherwise I would."
"Ensigns" has a lovely scene where she tutors the audience, via Picard, about the miracle of communication and it's an extremely well-written scene. Sadly, the clip a la carte can't be found on the same place where that fan-favorite fudge scene exists on about fifty billion channels...that one's also an exceptional scene that turns something rather mundane into an actual and surprisingly hypnotic event, but when the writers did something good for Troi that didn't involve her frothing over diabetes bombs, it really was the greatest.
More often than not, she gets a 3 and that's due solely to, as Q*Bert might say, "@!#?@!" scripts, to the point where the beige and gray background sets offer more creativity and depth.
Her best and arguably most genuine, in-character story is "Loud as a Whisper" as she gets to be everything: Empathic, tutor, liaison, having to go outside her comfort zone, even having a romantic moment - that feels real and genuine to the story. Even when the script is nudging her to be Riva's replacement**, Sirtis knocks it out of the park with nuance applied to the dialogue. (Reminding why she was cast to begin with. ) She gets the best romance-themed episode she's put into, and when it came to roooomance... on Staaaaaaar Trek, The Next Generation - the writers often had to battle Roddenberry's bizarre need to have gratuitous orgy planets and waaaaaay too often... Especially after the - shall we say - "misfired attempt" known as "Justice"... So keeping all that in mind, something with a modicum of nuance and depth in "Whisper" is that much more spectacular for being low-key and in a story that allows its concepts to simmer and breathe. Sadly, then we get to "The Price". The story is almost "there" with the manipulation of her but something doesn't quite work and it's not the fact that Ral is a charlatan. Similarly, "Face of the Enemy" is straining to work with a great take on the "fish out of water" trope but it just doesn't work.
** which creates a plot problem elsewhere, but putting that aside...