Which do you prefer, TV series adaptations or movie adaptations?

TV series adaptations. Because they have more time to cover more/all of the books aspects.

I’m begging for more miniseries. Good Omens is the perfect example of taking just enough time to tell the story correctly.
- The second season was fan service and unnecessary. Sometimes it's fine to end with one cohesive story and leave the rest to AO3.
  
  What does she have to do with TV series, I thought she was a politician?
  
  I will never be mad at more Jon Hamm.
  
  Plus it ended on a cliffhanger and season 3 is in jeopardy last I heard.

TV series. If it's good, I get to spend more time with it that way.
- I always said the Harry Potter movies should have been a series, each book getting a mini 6 episode season or something.
  Unfortunately that cast was great, and to be the time is passed. I know they're trying to do it again - but at this point I love the movies, they could have just been better. I don't have any hopes that they could recreate the magic.

Depends on what's being adapted. Some things benefit from a longer run time to cover all the good stuff, while other things benefit from a lot of the guff being cut and the story streamlined.

Depends a lot on the story complexity and pacing. The fact that a lot of adaptations are done poorly because they end up being someone else's story with only the veneer of the source material for name recognition, and that is true for both movies and tv/streaming series.
A fast paced novel like Hunt for Red October that is constantly moving the plot forward would feel stretched thin as a multi hour series. Thrillers often fall into the category, and so do short novels like Lord of the Flies. Even a series of books of these types this tend to be better as movies.
A slower paced book or book series is far better as a series, although fantasy often suffers from a lack of budget or falling into the TV adaption issues of adding content that doesn't really fit the source material to fill time. Not to mention a successful series can have be renewed and end up being a detriment to the source material after the source material runs out.
Overall the run time should match the source material pacing and content if it is a direct adaptation, and both formats introduce issues when that doesn't line up with common video lengths. I really like it when streaming series have different length episodes so that they can be the length needed to tell that part of the story!
- I really like it when streaming series have different length episodes so that they can be the length needed to tell that part of the story!
  I agree wholeheartedly and I think it's something tv producers are afraid to do or think people don't like it. Maybe it's just a relic from cable TV with set time slots. But no, you don't need to make that transition 30 seconds longer or add 2 minutes of scenery in between every shot just to stretch it to whatever minute-mark you're trying to accomplish. Same thing with cutting or rushing things; if I'm 4 seasons into your show, I like it enough to set aside an extra 15 minutes of my time to watch an episode that is properly paced and fleshed out, vs two that you chopped into awkward, rushed, flat 30 minute chunks.
  Stories are not uniform! Our story telling mediums shouldn't be either. Can you imagine if James Cameron tried making Lord of the Rings in 90 minute segments?

Depends what it's based on. It should have a similar runtime. So short story -> movie, book -> mini series. If it's like a series of 5 books I guess it can be a full TV show.
- One season per book seems to be what usually works best. That's why I think a Harry potter tv show of 7 seasons would be cool

TV or miniseries gives much more time to explore everything. I'm surprised it's not more common.
- Movies tend to have better monetary returns in both the short and long term for the movie and meechandising, so I can see why they would be a first financial choice.
  For actually telling a good novel length story a limited series tends to be best for sure, but most will have a smaller viewing audience and therefore less likely to be funded.

TV series would be best most of the time for adaptations. Miniseries specifically.

I actually agree with some people here. I enjoy mini series the most. This restricts the writer to stay closer to the source without going excessively out of bound with their interpenetration, allows for better character arcs and world building, without being restricted to 2-3 hours and no cliffhangers to sell the next 20 seasons. I prefer the 1 hour long episodes and then 8 to 12 at most. No season 2 unless it's another finished season in on itself.

With streaming the way it is, I would stop the chopping up of stories and start telling them in a new way. Shows are longer now and the quality difference is minimal, so just film and tell the story. Sitcoms and the like I get doing episodes but I think it’s time to review how stories are dispensed visually
- Peter Jackson releases the ultra-extended 176 hour cut of Lord of the Rings.

Miniseries. That way I can make a proper movie week.

TV series for stories I loved. (Preference for animation unless it's sci-fi)
Movies for stories I enjoyed.
I don't have a great deal of time anymore to just binge watch every show that comes across my table so I need to be more selective.

TV, I like to get all cozy like

Depending on what it is, TV series. Specifically animated. The exception to the rule would be anime currently running. I was severely disappointed by the Boruto movie being a collection of episodes from the anime, once I figured it out.

I wish that in order to make a non-original piece of film, there was a lengthy process where the filmmakers had to prove they had something new to say and jump through a bunch of hoops so that 17 groups of people didn't remake the same fucking book every couple of decades.
I like original stories.
imagine If instead of writing stories, most authors just wrote somebody else's story with the same names, sequence of events, and swapped out car for a horse and buggy. because the guy isn't eccentric enough.

TV series / mini series.
Tokyo Vice.
I rest my case.
- That show was so unbelievably boring idk how it got past the first season.

Depends. Is it a novel with a single entry? Is it a series of books with a lot of emphasis on world development? Is it an action video game franchise with little plot or lore? Or a video game franchise that prides itself on story? Is it set in the current world or in a wildly different fantasy/sci-fi setting?
In general, it's rare for an action videogame or book to convert well into a series because it requires lots of writing by writers who didn't invent the world and, vice versa, it's rare for a highly detailed fantasy world to work well in a movie because there's not enough time to do world building. Not saying it's impossible and there are great examples of both, but generally those are the ones that don't work out.