If you are interested in 4k, the VU Plus Zero 4k running one of the E2 images is very impressive! True hardware based blind scan and support for ASTC dongles. Definitely not for a newbie, casual user or faint of heart! The menus are complex, but tons of options. It is now my daily use STB.
Based on the multi-year history, I would avoid Android based receivers as the OS has proven not to be best suited for reliable and stable operation. This is too bad since the additional Android apps add a lot of value to a home entertainment system.
The latest Amiko may be a fine receiver for all I know, but I flashed my A3 with the original firmware after several bouts of reloading it with the Joe firmware, and it didn't hold up any better. Also, my A2 wasn't the most stable receiver in the world either. I don't think it ever boot-looped, but it would frequently get into a state requiring a power cycle when using advanced functions like the web interface, or sometimes even when blind-scanning. (Not unlike the A3 really, other than the lack of boot-looping since it wasn't an Android OS.)
If you want a basic receiver that works. The Amiko HD265 is a really good choice. It works and does what it supposed to do and no hiccups.
If you want something more advanced, I suggest you look into what Brian mentioned above.