I've tried to do work on various pocket-sized computers over the years (HP LX100 palmtop, Motorola Q, HTC G1, Samsung Sidekick 4G) and various netbooks and such.

The most productive device I've had is an Acer Chromebook. For me it is the typing speed, and having a nearly full-sized keyboard makes a huge difference. Adding an SSH client (though you can instead install the Linux subsystem) allows me to access my remote servers where I do development.

While thin and light, the Chromebook doesn't fit in a pocket. But it is not as if I'm randomly hanging out in coffee shops these days trying to do work.