I've been using Celtx, which is good because I can use it online and access the script from any computer, and it's free. I haven't felt like it really mattered what I use to write the script, though--these programs all more or less offer the same ease in writing. The main thing is the "shareability" of the script. Anyone can download Celtx so I don't need to worry about compatibility, and I can work with a writing partner more easily. I'm sure Final Draft has sharing features, but you'd have to all have Final Draft.
I'm writing a feature now for the first time in 8 or 9 years, and using a whole new process and working with a writing partner. It's been fantastic. I haven't been alone on it, which is really great for creating new material quickly and having it be more interesting. It's mostly involved talking about it so much it exists really strongly in my mind (it feels like we're talking about real people when we're talking about the characters). A lot of detail is present already. We wrote a scene-by-scene treatment, which was helpful.
The thing I'm finding very valuable currently, as I'm on draft 1.5 of the script (wrote half the script, noticed some big problems and then started from scratch): INDEX CARDS.
The main value of index cards, for me, is that it probably takes about two hours to index card the whole movie. You're working at the speed in which it would take you to watch the movie, and you're thinking about the balance and rhythm of the whole thing. It makes some things clearer and the impact of moving a scene to earlier or later in the movie is less abstract.
It helps with trying to figure out how the whole movie is balanced. Then, that coupled with already having a deep knowledge of the world and characters and information, makes it easier to write in a scene-by-scene fashion, which is ultimately what it comes down to in scripting.
I also use colored index cards so I can see how much time we're spending in each location, so that the film won't be visually stagnant.
I've tried writing in various places. Really, the only thing that works for me is staying at home, BUT, acknowledging the reality that it's going to take 6 hours to get about 1 hour of work done. That's just me, because I can't focus. I can't pretend that I can sit down for an hour and write. I need to carve out a large chunk of time on a consistent basis.
Oh, I also had to quit Facebook while drafting the script. If I had that, it'd be about 10 hours to get 1 hour of work done. Actually I'd probably just spend 10 hours on the computer and not get any writing done.
I used to be able to write while listening to music. I can't do that anymore.