Season 1:
10. Headhunters
I like this episode because it's the first where we truly see the twins seeking out the weirdness in Gravity Falls just to figure out the town's mysteries. It's got a nice mystery to it, as well as an awesome ending where Dipper outsmarts Sherlock Holmes. It's one of the funnier episodes in the series as well.
9. Irrational Treasure
Two words: Quentin Trembley. He made the episode what it is. It was fun to watch Dipper and Mabel solve a mystery, and have fun doing it, as well as to see Pacifica's reaction to the Northwest Cover-Up page, but Quentin Trembley made me die laughing. It's good that they didn't make him a "super-idiot", because that would have made him lame. It had some good secrets in there, but I picked this episode mainly because it was SO FUNNY!!!!! And how could I forget about the true story of Nathaniel Northwest? It made me crack up.
8. Double Dipper
The reason this episode is on the list is because it is a setup. Dipper and Mabel may have both lost their personal battles, but they both lived to fight another day, and defeated their respective arch-rivals within ten episodes. This episode's Gravity Falls oddity was an unusual stab at a classic sitcom occurrence. You'd never think it, but this episode is a cliffhanger.
7. Boss Mabel
This one had a good lesson (that management is hard work) and a good plot (that Mabel takes Stan's fez for three days). It was a nice return to Gravity Falls after a 4-month hiatus. It even had one of the funniest quotes in the show: "That man is a self-centered attention hog with no regard for human decency. Get him on TV!" But that's not why it's on the list. This episode is on the list simply because of the Stan Wrong Song. It is hilarious!!!!!
6. Dipper vs Manliness
A lot of people dislike this episode. The characters and plot lines from it do not appear much in the later episodes. Understandable; however, I disagree. Any episode that deals with the topic of real vs fake manliness automatically gets points in my book. And any episode of Gravity Falls also automatically gets points. It wasn't a bad episode, it just didn't fit into the storyline that well. Don't hate on this episode just because of the continuity; give it a chance because it has a great and understated message.
5. The Hand That Rocks the Mabel
This episode really fooled you. It gave you the impression that Gideon was a nice guy and Stan was just jealous...until the very end. I know most fans will probably disagree with me, but I liked Nice Gideon better than Evil Gideon. (Don't get me wrong, though. I also like Evil Gideon.) I also like this episode because it raises a LOT of questions, which have only begun to be answered at the end of the season. Remember: in Gravity Falls, there is no one you can trust.
4. Gideon Rises
Need I explain? This one I love for its purely epic ending. Some of my favorite scenes from the entire season include Dipper beating up Gideon with his bare hands, Stan exposing Gideon as a fraud, and Stan opening the portal to end the season. It may surprise you, then, that I did not like the first 3/4 of the episode. I think it boiled down to confidence. When the protagonists lose their confidence in themselves, as our protagonists did for the majority of this episode, I just don't like it because I almost lose confidence in them. Even after I've seen the ending. That is why it's not #1.
3. The Time Traveler's Pig
Why does this one place so high? Could it be the storyline of Dipper time travelling back to win the game and not hit Wendy in the eye? Is it the character introduction of Blendin Blandin, who will obviously be important later? (Here's a hint on that one: no. I strongly dislike Blendin; they made him too stupid.) What is it then? It's the ending. The ending of many of the episodes is better than the rest in my opinion, and this is no exception. It's Dipper's willingness to go back in time, even after he had already won, just for Mabel. (And Waddles' reaction to Robbie's caramel apple, as a little consolation prize for Dipper.)
2. The Deep End
This one is slightly higher than The Time Traveler's Pig, mainly because I like the storyline of a merman trapped in a public pool a bit more than time travel. It's more original. But the two episodes share similarities: Dipper is trying to impress Wendy throughout the episode, Mabel makes a new friend, and in the end, Mabel's plans to save her friend interfere with Dipper's plans to impress Wendy. Dipper does the right thing, but it turns out for the better in the end. I also like this one better because the end result turns out actually better for Dipper than if he had looked out for his own self-interest. In this case, he got fired along with Wendy, instead of keeping a job he really didn't want.
And number 1:
Tourist Trapped
Usually, nothing beats the original. The last six minutes of Gideon Rises are (so far) the only exception to that rule. Tourist Trapped was an introduction into one of the greatest shows on the planet, as well as a showing of how many ideas the writers really have and how far ahead they thought. This episode included Stan going behind his vending machine, Journal #3's debut, as well as Norman. It was genius, really, what they did with Norman. Dipper thought he was a zombie, and Mabel thought he was a vampire. 99% of writers in this situation would have made Norman be one of those two, but obviously, the Gravity Falls writers were that other 1%.
Season 2: (Top 5, up through S2 E10)
5. The Golf War
A lot of people are hating on this one. They say it's boring, or doesn't have enough secrets, etc. But I do not rank episodes based on the number of secrets they hold. I thought The Golf War was very funny, the Lilliputtians were a good idea for antagonists, and it set up very nicely for Northwest Mansion Mystery.
4. Society of the Blind Eye
How can you not love this episode? It cleared up so many continuity errors, and it was full of secrets. It was a completely original story line, too. It gave you this sense that the Gravity Falls writers know exactly what they're doing, as this was obviously planned out far in advance.
3. Scaryoke
This was the perfect way to welcome us back to Gravity Falls after that hiatus. They went to great lengths to not only remind us of who characters are and what they're about, but also to reference previous episodes and bring us back up to speed. This song also contains my favorite song from season 2 so far. (Hint: it's not The Rapper's Rap.)
2. Blendin's Game
I love this episode because it was a perfect blend of secrets with fun stuff. They brought back Blendin Blandin (and did NOT answer all our questions about him). They gave us a heartwarming story about Soos looking for a fatherly influence on his life. And they blended the two together so seamlessly. This episode brought my expectations for Gravity Falls to a whole new level.
And number 1...
Northwest Mansion Mystery
It's not about Dipicifica. I am neither a shipper nor a hater, but I am looking forward to seeing them as friends. It's not the apocalypse, either. For some bizarre reason I didn't like the endings of this episode or Dreamscaperers. This episode, like Blendin's Game, managed to seamlessly blend a monster-of-the-week story with a load of secrets about the Northwests, while also throwing in some Dipicifica moments without getting them together. It also showed some strange changes in character, most of which, I hope are permanent.
