I like a lot of episodes, so it's difficult to pick. And my favorites change depending on my mood.
Right now
Season 1:
Memory - It's one I remembered from my earlier viewings. Not really arc-heavy with Rick stuff (which I love), but it's just entertaining. I like how Fi pushes too much (sometimes a character's greatest strength can be a weakness, too), and Clu was funny and I liked Cole "joining forces" with Fi. The adults and "maybe it was the heat" backtracking was predictable enough that it didn't even disappoint me.
"Angel" - It's fine as a stand-alone, but I like it best for introducing Gabe who keeps existing long after the episode is over. I like Fi being wrong about the angel being a demon and I
adore her calling the angel creepy - he really was. But I go crazy of the unnecessary cryptic-ness of the angel. We know he's capable of speech, so why not just explain himself to Fi? Much easier and simpler. Wouldn't be much of an episode, I'll grant you, but far more logical.
Season 2:
"Nightmare" - I love Jack/Fi moments, and this episode has them. Plus we get insight into Jack's psyche with his nightmares (and he does he know what happened or just imagine it?), which is great. I recall a long while ago reading someone say that Fi makes friends of the kids they meet, and Jack makes younger siblings of them - he's the protector and comforter and so on. A Clu/Fi
is there, so that's good. And I really like how Clu is just jazzed about them all sharing a dream. I was a bit surprised that Carey made no appearance, but I guess he's not connected enough to Jack (or his cousin) for that?
"Second Generation" - Fi got a date. And I like this guy: he's cute, intelligent, articulate, and reasonable. I like his reaction to his discovery and I like him sending the genetic code of a rose, and he just works as a character to me.
very fleshed out.
"Banshee" - Of course, I love this one. More implications about Rick and the nature of his death, which is always good. The fabulous scene where Jack finds Fi. Fi and her bravery and strength, fighting for her grandfather and showing her nature is a fantastic scene. Plus, I really, really like the song "The Rock."
"Strange Geometry" - Good emotional content for both Fi and Molly. And Fi finally learns about Rick's interest. We get to see her strength and integrity in her decision not to keep souls trapped forever. And I really like the character of John Kane in this ep.
"Destiny" - Look, I know I'm in the minority, but I don't care about Bricriu, himself, but what he brings out in Fi. But I getting more info on the mystery of Rick is great. As the show goes on, you just get more and more of sense of how big, how powerful the forces arrayed against Rick (and now against Fi learning about Rick) are. I will say Bricriu was legitimately menacing towards the firefighter in this ep.
Honorable mention:
"James Garr" - The emotional content of this episode is great, but I did not like the ending.
"Twin" - The episode is good, but the ending is such an incredible letdown. Especially now that I know how it was originally planned to be. There was so much work up to what happened to Rick, and then we got no answers.
And I can't comment on Season 3, as I have not yet rewatched the eps yet. Right now I'm just so fixated on the original S3 storyline planned. I want
that story.