I put together an olkb planck 40% kit years ago, and it's still my main keyboard for day to day use. (programming, gaming, writing, anything really)
The main thing I like about it is that I can just put it in my backpack and carry it with me. It's nice to take my laptop to a cafe or library and still have my good keyboard with me.
There’s a couple 40%-ers in the comments but not nearly enough. It took me years to learn to properly type, but once I did, I fell in love with a 40%. There’s some cool designs out there for small keyboards, like the Minimi 40 with a combination lid & wrist rest (not released yet, but it’ll be glorious once it’s finally available).
I have a simple planck eotb, and carry it everywhere I go. It's really convenient.
I think I got used to typing on it in only a couple of weeks, but spend the past few years tweaking my custom ambidextrous layout.
Some of my personal favorites are:
having backspace+ctrl combined on one key, enter+shift combined on another key.
Having enter and backspace on both sides of the keyboard, so I can use either hand to use them
Having a single hand numpad when holding a layer key. Very practical for number stuff.
Putting any computer to sleep, or changing volume without having to look for the right key on my keyboard.