What I use, and therefore generally endorse.
For the last three years I've used a first gen Dell XPS 13. It's made of aluminium and carbon fiber which makes it very strong and very light. If you measure the thickness at the edge it's slight thicker than a MacBook Air, but at its thickest point it's thinner than the same Air at its thickest point. Even after three years the battery is amazing and the machine is still stable and fast.
Back in the 1990s and early 2000s I used to build my own machines. I enjoyed sourcing the parts and the whole build process. These days I can't be bothered with all that. I generally go with whatever I can find that fits the spec I want at a price I want, safe in the knowledge I can customise it to my tastes later. Right now I'm using a Viglen Genie. It's a core i7 with 16gb RAM, and a 256gb SSD. I have a 1tb HDD for data, backed up to Backblaze, and a 650gb HDD which I use as a kind of temp drive, or scratch disk.
I use two AOC 21.5" IPS monitors on a dual-arm mount. They're fairly inexpensive but they're good enough for what I want. I'm not a gamer, and only an enthusiastic amateur photographer.
I have something of a tradition where I re-purpose my previous desktop workstation for use as my local server. Right now I have an old Dell Inspiron, it's a dual-core with 6gb RAM. It houses a 128gb SSD with Ubuntu 18.08 Server running on it. A 2tb media drive, which I backup periodically to an external drive, and a 700gb drive I use for storing and processing files on their way to another location.
Backblaze for backups, and Digital Ocean for VPS.
Besides a collection of Russian cold-war era compact cameras, a GoPro (and a few clones), my photography is either with a Nikon D90 which still holds its own after nearly ten years, or a Fuji X100 which is a joy to use and perfect for carrying around one's neck all day.
My pride and joy, an original Prusa i3 MK2S which I've recently upgraded to the MK2.5. I bought the kit and learned so much building that I've been able to confidently tackle any problem that has arisen. Plugged in to is a Raspberry Pi Model 3 running Octoprint with a RPi Camera Module to allow for remote viewing and timelapses.