Right now ipq807x isn't usable yet, as there are still missing pieces (most importantly, ethernet/ switch support, but also a lot more than 'just' that) and without support for any actual device so far. Personally I'd still expected this to be the most promising platform in sight.
Technically mt7621a+mt7915e has beaten ipq807x in terms of OpenWrt support, but I have no idea about the extent of what this actually means in terms of 802.11ax performance/ reliability - and I have quite serious concerns about mt7621a's viability for router uses and the demands 802.11ax requires for that.