The OpenWRT wiki pages for the routers usually has some detailed info about the hardware. That won't tell you about hardware problems they might have that they didn't investigate but you can usually find photos of the boards to see what's there. [1][2][3]
https://wikidevi.com/ also has detailed information about what chips are used, often gathered from FCC filings. Atheros, Broadcom, etc. are a lot more trustworthy than D-Link and Netgear. Once you've identified a router as having an Atheros SoC and a firmware update format supported by OpenWRT, you really only need to worry about it having bad power supply and antennas.
