I can recommend the Netgear R6220 which is supported since 18.06. It is MT7621 based and has 128MB RAM, 128MB flash (newer versions only 64MB), 802.11ac (up to 867MBps), 802.11n (up to 300MBps), 4 GBps LAN ports, 1 GBps WAN port. Available for ~40-50 EUR. It is worth the price.
OpenWrt is missing flash layouts for newer versions in the 18.06.1 release. The issue has been analysed already and the new flash layouts are available for creating new images:
It is possible to build your own images based on the required changes but I hope that those changes will find their way into future images provided on the OpenWrt website.