Is there a favorite one I can buy now? Or a least unfavored?
The software and motherboard schematics are totally open. It includes an mPCIe wifi card (Ath9k) specifically to avoid binary blob firmware.
If something refurbished is okay, go for a X200; they are pretty good machines. Here's the best part - a Chromebook, without the proprietary Mali drivers, it slow as a piece of shit; an X200 - I can watch a tear-free full-HD movie while compiling something in the background, with both cores at 100%.
Libiquity, Tehnoetic and Vikings still sell those laptops. Or flash one yourself, it's not that hard, and you need like.. 100$ worth of equipment.