2019-6-4: My (John Nash) current primary “working” machine, called J6, is a Sept 2011 tower, which has served me well and is still a useful and well-balanced computer for my needs.
I like a fairly big screen. At one time J6 had two monitors, a 24“ HDMI and a 20” VGA, but I've found just the 24“ is fine. Smaller screens (as on my laptops) are not as helpful for writing and programming. I use headphones for audio – no fancy speakers.
I also like a decent keyboard as I am a touch typist. However, it is useful to have a numeric pad. While I'm happy with a lot of pointing devices, I find a mouse easiest, and use my left hand for this, though I am right handed. This seems to avoid some wrist stress I had a decade ago when a friend suggested this simple change. (It also inhibits folk from using your computer!)
J6 has the following very edited setup:
These could each consume a lot of discussion. I am prepared to use them as topics in Linux Ottawa meetings and put a summary of the discussion here.