Season 2: This is peak comedy with a plethora of great episodes, particularly in the first half. Great character development and strong opening and closing episodes.
Best episodes: Slap Bet, Swarley
Worst episodes: Columns, Moving Day
Season 1: Same applies for this, so I had trouble choosing between the two. I guess, we're still getting to know the characters here and Ted does get a bit too Teddish in some episodes but other than that it's also peak.
Best: The Pineapple Incident, Drumroll Please
Worst: Belly Full of Turkey, Life Among the Gorillas
Season 9: Shocking to some, but I find this season's wedding setting incredibly creative, and I loved the ending and all the Mother episodes.
Best: How Your Mother Met Me, Gary Blauman
Worst: Slapsgiving 3, Bedtime Stories
Season 3: Loving the aftermath of Ted and Robin's breakup, a decent season overall, just not wow I guess.
Best: How I Met Everyone Else, Third Wheel
Worst: Little Boys, The Chain of Screaming
Season 5: Not a fan of Barney and Robin together, but we did get some funny episodes and a glimse into the Mother.
Best: Girls VS Suits, Of Course
Worst: The Sexless Inkeeper, The Rough Patch
Season 7: This is a strange one, because it does have a great opening and closing and some very cool episodes. Some plot points and character arcs give me the ick though.
Best: Ducky Tie, Symphony of Illumination
Worst: The Rebound Girl, Field Trip
Season 6: Overall a mediocre season. Zoey is an... interesting character, which can make many people hate the season and I get it. Marvin's death and its aftermath gave us some great character development.
Best: Bad News, Oh Honey
Worst: Garbage Island, The Exploding Meatball Sub
Season 4: Nothing stands out for me in this season. It's not terrible but there's nothing that memorable for me, plus several fillers.
Best: Three Days of Snow, The Front Porch
Worst: Mosbius Designs, Old King Clancy
Season 8: The main reason for it being so low is that it really destroys some character arcs, especially Robin and the whole thing with Patrice and the proposal, and poor Victoria whose only great moment is summarised in her last line. Also, many, many fillers.
Best: Farhampton, The Ashtray
Worst: Who Wants to Be a Godparent, Splitsville