My take is that nobody is doing better than Pi in terms of the community Pi targets, e.g. students, amateurs and greenhorns alongside professionals. There's a critical mass with Pi that attracts industry players to be on the platform with what counts for decent support in the embedded world, e.g. Microsoft and Canonical.
Always. Everywhere. Wanted 25 units to teach a robot class to some local kids at the Hackerspace. Had to buy 3's instead. Even if I'd placed 25 separate orders, the cost of individual shipping on each vs the cost savings of the combined shipping on the 3's put the price within spitting distance.
Pi zero is an ad. A loss leader. A way to have an answer, any answer, to the flood of $7 Allwinner wonder-boards on AliExpress.
The Zero is a very different devboard, though - you will need to invest in assorted adapters and hubs if you want to connect it to just about anything other than power... it is useful in small spaces, but for anything else spending a little more to get something like the CHIP is well worth it, and for use a small PC, going to the RPi 3 is probably wiser.
The Raspberry Pi 3 is available from many vendors for $35 + sales taxes. You can pick it up on our site for £32 including VAT (that's EUR30 before taxes or EUR36 including taxes): https://shop.pimoroni.com/products/raspberry-pi-3
Texas Instruments am335x also is a popular chip with upstream support (Beaglebone Black & Olinuxino am3352-som and quite a few other vendors have modules based on it.) If you want a canonical list, look in the kernel arch/arm/boot/dts source: https://git.kernel.org/cgit/linux/kernel/git/stable/linux-st...
Actually it looks like there are quite a few Allwinner devices listed (look for sun__...)
ODroid C2 and XU4 have been making progress, though last I saw they weren't really stable yet. I think HardKernel, the manufacturer, is providing some level of support for the mainlining effort.
Next Thing says the C.H.I.P. (or at least the C.H.I.P. Pro) runs mainline Linux, but that's not really comparable to the current Raspberry Pi.
Does it have support for the graphics though? That's the first big stumbling block these alternate SBCs run into. Without support for graphics acceleration you won't be able to play video properly or run fancy desktop apps. It's a huge drawback these days.
