Lynda Barry's comic says it better than I could.
Favorite part- when it's like I'm a kid playing.
Least favorite part- when the Two Questions butt in...
@onyefrankie Oh editing 
I know I'm going to find grammar errors and typos
@mrtoontastic I love all those feelings too 
It's the best high
@minerrale Yes! not being able to word properly is so frustrating!
@Leon the idea that you'll never finish is so real! Especially when you dedicate so much time and energy to it and you get stuck!
@CremeChronicles I can understand the actual writing part being the least favorite part. For me there is some sanctification seeing the words come to life before me.
@JenniferBourne That comic says it all! Thank you 
I love the research part of writing the story.
The re-writing part when you have to throw away good for better is the least enjoyable.
Favorite: When I make a theme for a story and make specific moments in that story follow a theme on purpose, but then another part of the story that I didn't mean to make go with the theme goes with it anyway and then I think to myself "my god... I'm accidentally brilliant!" XD I also just love when I stumble upon that perfect idea that I want to make into a story and when I first get to put that idea to paper. Character building is also a blast, too while world building has always been less important to me.
Least favorite: When I lose steam on a long-form story because I'm so used to writing short and simple short stories.
Favorite, coming up with the scenarios and major moments. Least favorite coming up with the details of the world and the moments leading up to the major moments. In a way that makes sense at least. I forget some of my own plot elements TOO MANY times.
@vicar_comic It can be hard to change scenes you really had your heart set on 
@ratscout of all the ways you could be brilliant, being accidentally brilliant probably feels the best
@fighterxaos I tend to forget things too so I keep a notebook to write everything down in it when I think about them.
Wahahaha. I think we're opposites, then. I like editing the most, and my weakness is... writing that first draft. Guh. But that's just the literal "writing" part.
My favourite part of writing(as a whole) is doing all the puzzle work to figure out how the plot should go, and seeing the pieces finally click together in a satisfying way. When a story that consists of multiple pieces becomes a coherent whole, you get this immensely rewarding feeling. It's quite awesome to see your plot become the thread it should be - instead of a haphazard collection of events.
And my least favourite part of writing as a whole is... being unable to write as often as I want..
Coming from a comic writer who has also written stories, my favorite part is coming up with an idea that really works for me -- maybe just a basic concept or something similar; just an idea that really inspires me and makes me think and resonates with me. This also includes tying up and connecting events in a story, particularly when these events work better with previous events that I had at first expect.
My least favorite would be getting stuck. Trying to tie two events together and not being able to get past that mental block; lacking inspiration and being unable to motivate myself to get beyond that.
@xanedis I am beginning to like editing, it gives me a chance to reexamine my work and look at how I could improve it
@spooktacularprize I can completely understand trying to motivate yourself past mental blocks!
Favourite Aspect of Writing
Writing the main frame, especially the detailed ending, and imagining how awesome it all is.
Least Favourite Aspect of Writing
Filling in the rest and struggling to keep facts and plot details consistent.
This is especially true when it comes to writing mystery stories - for those that are doing so, I salute to you.
Trying to fill that space between the awesome scenes in your mind can be the most frustrating part for me! Though sometimes it leads to a scene developing better than you thought!
I used to have that same problem, but it mitigated over the years by practice. Now I'm feeling relatively confident in writing those middle parts. You just have to make sure that your every paragraph feels like they're tightly connected to the main story, instead of having some just loosely hanging on to the general story structure.
That said, I speak from the viewpoint of an outliner(not a full-blown one, I tend to discovery write my characters and those "middle parts" you mentioned). It might be that your writing method is a bit different, but the same principle from the first sentence applies - just write. You'll get better. If you feel up to it, I would recommend reading about writing(but if that puts you down, just write), however, even with all that knowledge that you could gather, you'd still have to learn to put it into practice. And I can't stress enough how much a good night's sleep will help you to write better on the next day...
sighs Sorry. I got started on a rant. Just keep in mind that writing is a holistic art - a lot of things influence your performance. XD
I agree with the "good night's sleep" part. Sleeping is extremely important when writing. Not only are you better focused when you're really awake, but dreaming helps your brain process the informations of the day (including your story) and piecing it together to make sense. That's the main purpose of dreaming, in fact. And it helps a lot with finding plotholes and filling them up!
@xanedis in this case, ranting is valuable and appreciated!
@minerrale Man I wish! I hardly ever remember my dreams 
Ah, no, that's not what I meant ^^" all of this is done by your subconscious while you sleep, you don't have to remember your dreams for this!
Well it's better if you do, mine gave me the basis of Abby's Hope AND of the other book that it talks about 
but it's not necessary at all for this process.
It's basically your brain working while you're looking away
I might not have been very clear either ^^" sorry, I'm still not very comfortable with english, especially when I'm talking to people and not writing a story since the style is not the same
No worries! I appauld anyone who takes on English as another language. It's difficult (especially when someone doesn't read get you said right )
I like that I can just pour my imagination to my writings when I'm unable to draw it.
But what I hate is that I need to go back and fort to a couple of dictionaries just to find the 'right' words. Even if I do, my tenses is all over the place, so it's frustrating at times. Plus, if the things I searched on Google for reference doesn't exist or simply lacking, that's gonna put me on edge at times.
I also someone that have low motivation, so when my stories doesn't go well, I usually will lose my interest at that moment until I'm able to go back up again. Somehow it feels pathetic 
.
But hey, I still love to do it.