So... here are mine, though I gotta mention that in terms of favorites, I have often changed my mind completely before... but that happens with me on other shows/video games/etc. as well...
But here are my favorites:
My top favorites will pretty much always be Lifty and Shifty (yes, I count the two as basically the same character) for being those two thieves with the greatest facial expressions, voices and laughs ever and for participating in some of the show's greatest episodes. I just love it whenever they appear, almost always trying to steal the first thing they see... with usually horrible results. But even for thieves the two had a lot of kind moments and occasionally managed to earn money by actually selling things (not only do they help Disco Bear with his baldness problem in "Easy Comb, Easy Go", they even survive said episode). And how do I put it... two gruesome deaths for the price of one? Yeah, pretty messed up that fatality rate would have an effect on me liking a character a lot... but you know you have two special characters when they have the lowest survival rate out of all the main characters so far (only Shifty has less).
Next would be Lumpy, without whom the show simply wouldn't be what I've come to love. I just love his especially stand-out appearance, his awesome voice (particularly when he screams) and the fact that by design he's usually one of the kindest characters the show, yet the poor old moose just causes so much shit to happen. Also, his deaths and injuries are almost always gonna be well-known for one reason or another... lastly I would like to add that the rather... irrational fans with their nonsensical and hypocritical hatred for him (Lumpy kills my favorite characters, I hate him! Flippy kills my favorite characters, I love him!) only make me love him more.
Third would be Disco Bear for his absolutely hilarious voice and attitude. Sure, he acted like a twat back in the first two Internet seasons (I heard that even the creators themselves didn't like him back then), but from the TV series onward he has only been received better. Like the two (or three) above, I love almost every second of his screentime, mostly because you know he's gonna act as smug as always and say something like "Oh yeah... 'how!" for good measure.
As for least favorites? While I don't really hate any of the main characters (the only ones I genuinely hate are Mr. Pickels, the Ants and that goddamned turtle from "Letter Late Than Never", but neither are main characters... and I blatantly refuse to acknowledge Mr. Pickels as part of the main cast), there are some that I am not that fond of in comparison to the rest, which I'll talk about here:
Mostly it would be Cro-Marmot for being as flat as inhumanly possible. I don't know, but no matter what sort of Handy-esque "Offscreen Magic" you're trying to sell me, having something akin to a static image appear in this show at such a rate almost reminds me of the infuriating fact that Tanooki Mario and Cat Suit Peach were DLC content in Mario Kart 8 and both were reserved their own character fields. But unlike those two, I don't necessarily hate Cro-Marmot... he's just criminally boring to watch. Get him out of that ice block and make him actually do things like any other character and he'd be more well-liked.
Then comes Splendid for... well, fucking up far too much with facepalm-inducing amounts of stupidity not even possible by Lumpy. Now, THAT fact alone I have not problem with, I love it when crazy shit happens in HTF (it's what I basically watch it for), but it's the fact that in a show where just about anything can die, this particular rodent almost always comes out unscathed, which in this show makes him look shockingly boring as a result... and I don't know why, but I will never forgive him for intentionally obliterating The Mole in "Gems the Breaks" (thank goodness he actually died there for a change).
If I had to add a third one it would have to be Lammy by virtue of being the owner of the aforementioned Mr. Pickels (whom I still refuse to consider an actual character at all) and for not having had enough screentime so far to make a better impression of herself, with a chunk of said screentime having her unknowingly kill other characters... only time will tell if she gets better over time. That being said, I do like her appearance and her adorable bleating voice.
Favorites:Nutty (he's the funniest one in my opinion), Flaky (She's hilarious), Splendid (He's a really funny take on the superhero genre), Giggles (What can I say? I have a ginormous cartoon crush on her lol)
Least favorites:Cro-Marmot (He doesn't do anything), Disco Bear (How he constantly flirts with the female character gets on my nerves), Mime (I just don't think he's that funny), Lammy.....Please don't get mad at me for this one, but I feel like they added the HTF equivalent to the Great Gazoo (a weird character who appeared out of nowhere on The Flintstones). A lamb with a talking pickle? That's kinda weird
"A lamb with a talking pickle? That's kinda weird"
Weird you say? Reminder that this is HTF we're talking about.
The show's always been weird but all the characters (until the pickle) were animals. This isn't VeggieTales, Sausage Party, or Annoying Orange:Why is a vegetable suddenly walking around like the other characters? It's kind of like when they added aliens to Indiana Jones, the series was always a bit out there but aliens are pushing it a little due to the fact that it's not sci-fi.
I would love to think, that Lammy is just crazy. But since Royal Flush it's pretty obvious, that Mr. Pickles is indeed a real being.
I love that episode! I was so shocked to see childish characters like Giggles and Lammy doing something normally associated with adults like poker. That's kind of funny if you ask me, plus the episode has literal toilet humor in it lol. I don't however like all the comments on the YouTube version of the video about Flaky being on her period (That's a little disturbing to think that so many people have thought of that, if you ask me)
My favorites characters are Petunia and Flippy My most hated are Nutty and Disco Bear