I personally do not aim for either. Instead my goal is to write a scene each sitting. A scene may be 2 or 3 paragraphs or 10 or 12 pages, depending on the story and scene in question.
A lot of people read my writing articles and assume (incorrectly) that I'm advocating aiming for specific word counts. This confusion comes from the fact I'm answering a question that specifically asks what my average word count is and how I reach those word counts, resulting in I answer that question by writing an article based on writing in comparison to word count. However, almost no one ever asks if I personally AIM for specific word counts or not. No. I don't aim for any certain word count goals.
The only reason you ever hear me say I average so many words a minute/hour/day, is simply because people want to know the word counts. But an average is just that: an average. I have days I barely get 1,000 words and days I reach 17,000 words. Both are extreme ends that I don't do often. Average only means you take the lowest number and the highest number, add them together, then divide them by whatever figure (seconds/minutes/hours) is needed to get the average in question. So if I said I averaged 5,000 words a day, it DOES NOT mean I write 5,000 words every day, it means 5,000 words was the result of adding the lowest number to the highest number and putting that number in the formula to get the end result.
So, if you wrote 50,000 words in 30 days, you take 50,000 and divide it by 30 to get an average of 1,667 words written per day. But you could have had 5 day of 100 words and 1 day of 30,000 words, and several days of 500 words. Just because 50,000 words in 30 days equals and average of 1,667 words a day, doesn't mean you wrote 1,667 words every single day.
I think most authors do this, where they say they write an average of so-and-so words a day, but then new writers look at that and mistakenly translate that to mean the author AIMS to write a specific number of words a day, when it's unlikely that's what the author meant, when they said the average a certain amount of words per day.
Does that make sense?
Hours per day on the other hand is quite different (for me). Because I'm a "career author" doing this as my full time job, (and publishing 4 or more novels a year and 4 or more short stories a month and 2 to 3 non-fiction articles a day) I've set aside a very specific work schedule. Just like any other person with a job, I have a specific, set schedule of hours I work each day. I get up and go to the office at the same time each day, have assignments/tasks that must be completed, have assigned breaks and lunch break, just as if I was working at WalMart or McDonald's.
This means I get up at a certain time each day, do my writing at a certain time for a certain amount of hours, take a timed break, then it's off to do more writing or editing or researching, depending on the day and time. In the end I work 3 shifts a day of 4 hours each, with a 15 minute break every 45 minutes, and a 1 hour break every 4 hours. For a total of 12 hours a day of writing and editing.
But even with this schedule, it can be pretty fluid. Say, today's assignment is to write one chapter for this novel, then editing one chapter for that other novel. If it takes me only 2 hours to write the chapter, that leaves me with 2 hours before my next shift starts. I may just move right to my next assignment, the chapter from that other novel that needs editing. I could have my entire day's planned assignments finished in the first 4 hour shift, meaning now I am done for the day and have the remaining two 4 hour shifts off. I may use that time to move on to writing/editing the next chapter, or I may take the rest of the day off to play video games. Or that one chapter may take me the full 12 hours to write and I not have time to do the editing assignment, in which case I may go into overtime and work more than 12 hours that day or I may move the editing assignment to the next day.
So even though I've set aside specific times to do things, I've also assigned myself tasks and goals. The tasks and goals are always in terms of scenes and chapters, and never in terms of word counts or hours needed to finish it. I never think "This scene needs to be 2,000 words long", but rather I think "This character needs to achieve this goal in this scene" and then I write until the scene is finished regardless of word count or hours needed to finish.
My method of setting aside a work schedule would work well for others who are doing writing as a full time career, but for people doing it as a hobby or any one who just has one book they want to write with no plans of doing more, this sort of schedule would be impractical.
Years ago, when writing wasn't a career for me, I used to set aside small chunks of time throughout the day. An hour first thing in the morning, before even getting out of bed. Another hour during lunch break. Another hour just before bed at night. That was what I usually did back then.
In the end, I think each writer is going to have a different method that works best for them, and the only way for them to find out what that method is, is for them to just try out every method until they find the one that fits their life, their writing goals, and their schedule.