Top 3
Out of Gas
Objects in Space
War Stories

Maybe. The most obvious is you will know the fates of the characters, as well as the fact that River's past is a big mystery throughout the series, which of course was fully revealed in the movie.
However, there are plenty more stories and mysteries the show was able to tell in 14 episodes that the movie couldn't.
The budget is smaller on the show, and it does lean much more heavily into the western aspect of the franchise, but I do feel it is superior to the movie.
So many stories, so little time.

I actually saw Serenity for the first time the other day. It was good, but I haven't seen any of Firefly yet. By watching it first, did I screw anything up for when I actually watch Firefly?

I'd have to go for that one, too. The three different timelines being shown made from some engaging television. Plus, Mal seeing Serenity for the first time is such an unbelievably beautiful moment, and it really solidifies what Serenity represented for Mal: freedom.
So many stories, so little time.

Out of Gas, hands down.

@Beren44
You got the branch scene wrong. There was actual a gun lying on the floor in the cargo bay (which I found actually kinda odd, but on the other hand it was Jaynes gun, so not that far-fetched) River saw it just in her mind as a branch!
I have two theories where that memory/distorted picture in her head could came from:

1. The subjects of the human-weapon program where maybe threated with some weird mind suggestion methods, in which they were trained to see weapons as common objects- hence why river is shouting "It's just an object" several times.
2. The wood we see a glimpse of is the same one we see behind the oudoor classroom on Miranda in Rivers flashbacks.
   I personally prefer the first theory, but it also could be a mixture of bothor some other alien memory - who knows - they so heavily fcked up poor Rivers brain, that not even she could tell.

Today I was in the mood to watch something very funny, but didnt really know what to pickin a collection of thousands of movies and series that easily can get difficult
.
I watched Slither just the other day and then thought wtf just stick with Fillion and watched "Our Mrs. Reynolds"!
This one cracks me up every time, the first mins after the Intro alone are so god d*mn hilarious, my stomach always hurts! I've always thought this is the best fun ep
of the showand how's the name of the best drama one? Stuck in Space? No. Lets check imdbYeah of course "Out of Gas", fool.
I came across this thread where many ppl just think the same, and reading all the praise here I got really in the mood to also watch "Out of Gas"then I rememberd oh yeah I didn't watched "Serenity" on my last marathon(4-5 months ago), because the HDD with the copy of it was broken, so watched "Object in Space" and "Serenity" -> Just finished and I just wanted go to sleep after "Our. Mrs Reynolds"
And now it feels kind of incomplete in my headso I'll start with my third (full) marathon this year tomorrow
It's always like that, if I remember correct three times I just wanted to watch Mrs. Reynolds, I did and it lead to a marathonI might have serious issues
But in my humble defense, I have to state, I watched Firefly for the first time in 2012, so ten years later than the Op her/his(?)annual marathons, so its clear I have to binge like three/four-monthly!
So and whats the point of my lengthy story regarding the Op's question:
Just all of it!

It hard to name a favorite, they were all so good! I would have to agree about "The Message" being the weak link in the whole series, though. Even saying that, there is a bit of poignancy, if you have read the back stories about the show. The scene when they were all standing around the coffin listening to the recording, was shot JUST a few moments after they all got word that the show was cancelled. If you go back and watch that part, it is very touching, the oh so real camaraderie between the cast members just shines. They are all truly upset.
And I would agree, Objects in Space was probably the next least favorite of mine. I still have never heard anyone explain the scene with River grabbing the branch, and it turning into a gun Anyone have comments about that?
~Oh, I'm well aware it's not a picnic, Mr. Save the Day~ (Fitz, Agents of Shield)

I really like
Ariel
, from the planning of the heist, to the heist itself ("We applied the cortical electrodes, but couldn't get a neural response!"), to Simon saving a dying patient, to Jayne's betrayal and ultimate redemption at the end of the episode ("Don't tell 'em what I did!") Plus, we get to learn a little more about River's condition and what the Academy did to her. Great episode all around.
I also love
Shindig
, mainly the scenes on the ship with Badger. ("That there was exactly the type of diversion we could have used.")
My least favorite is
The Message
or
Objects in Space
. The Message is kind of pointless, although I love the opening scene with Jayne's hat. Objects in Space was a bit existential, which made it a great River episode, but I never really could get into it. I found it quite boring. Plus, Jubal Early just annoyed the hell out of me.

Arya: Lots of people name their swords.
The Hound: Lots of c_nts.

Mrs. Reynolds, Hearts of Gold and Trash (just Mal sitting on the ground naked saying "Yeah, that went well.").

If you don't like the show, stop watching it!

Definitely "Our Mrs. Reynolds" the chemistry was amazing between Fillion and Hendricks. Love when women outsmart men in TV shows which is not so often in this patriarchal society.

I just finished my annual Firefly + Serenity marathon. My favorite three Firefly episodes are:
Out of Gas
Objects in Space
Trash
I actually really like all of Firefly's episodes but I like those three the most.
How do you know it's love if you've never been in love before?

Out of Gas, for the back stories.
And, Objects in Space, probably my favorite. Early's last line makes for a fitting series conclusion that will have to do. I still get teary-eyed when he says it.

What in the wide, wide world of sports is a-goin' on here?

It's either Out of Gas or Objects in Space. I love both of them to death.

Out of Gas
is my favorite dramatic episode.
Our Mrs. Reynolds
is probably my favorite comedic-leaning episode. I really can't choose between the two, because they both represent such a great effort.
And FURTHERMORE, this is my signature! SERIOUSLY! Did you think I was still talking about my point?

Out of Gas

I see you even mentioned "Shindig". That should be the yardstick with which hardcore fans of the show should be measured.

Hmm, I don't think I have an absolute favourite episode, but I really like Out of Gas. That episode was awesome, with a great soundtrack, and cinematography. Ariel was also a really good episode, the Hands of Blue were great villains. Objects in space was also great. So was war stories, the message, and serenity part one and two. Better add in trash, heart of gold, our ms reynolds, safe, and defiantly jaynestown. Oh, and also bushwhacked and the train job! They were great. And I can't forget shindig. That was pretty great.
These are pretty much my favourite episodes of the entire show. They were really the highlights for me.
Wait a minute.

Objects in Space b/c I like the Jubal Bounty Hunter character. He had an interesting and strange outlook on life. I wish he lived I could see a series built around him.
I liked 'Our Mrs. Reynolds' mainly b/c I thought Christina Hendricks was extra sexy in that role, moreso than other roles she's had.

Yeah, I think we can all agree that Out of gas is an absolute masterpiece. The way every story is intertwined and the way the main conflict of the episode is shown sort of backwards, in two different timelines; it just keeps your attention for the whole run of the episode. It's very emotional but also technically accomplished.
I agree that
Out of Gas
is probably the best episode. My favourites are probably
Ariel
and
Trash
. If I'm just pulling one out to watch, however,
Serenity
(the pilot) usually wins.
"It's a real burden being right so often." Captain Malcolm Reynolds, Firefly

Yeah, I think we can all agree that Out of gas is an absolute masterpiece. The way every story is intertwined and the way the main conflict of the episode is shown sort of backwards, in two different timelines; it just keeps your attention for the whole run of the episode. It's very emotional but also technically accomplished.

On the episode Jaynestown
The end conversation between Nathan Fillion & Adam baldwinwhen Nathan says..
Every man ever got a statue made of him was one kind of a son of a bitch or another
Ain't about you jayne it's about what they need with excellent background score
this episode is my favorite because of the bad-ass character for the very first timeis shown timid & fragilesimply loved it
Relive the moment again
Firefly- Jaynestown episode (with English subs)
http://visualnama.com/video/132/firefly-jaynestown-episode-07/

Yeah out of gas. But also objects in space. Because I think it was a significant episode for River. And the whole Lion thing.

Do you have a favourite episode?
Yes, all of them
Honestly though, it is very difficult to pick out just one.. it feels so exceedingly unfair to the others, hehe.
Let me show you the deep raw passion of unbridled sexual frenzy. But Lucy im British