After trying many models, I found the most practical overall for me is a ThinkPad T500 (highest-res tall-screen version, modded with a transplanted T60 keyboard, and the T-series CPU replaced with P9600 or P9700), and running Debian GNU/Linux with Xmonad.
Bonus: at around $100 apiece, I can afford a few spares.
The main downside is that it's noticeably vintage, which, given current industry ageism, isn't good optics in the hands of someone already 30+ yo. So I should try to spin the vintage as a hipster fashion thing. :)