I have the A500+ using an Indi ECS, no issues. The picture is a lot sharper than when I had a SCART setup.
For quality from bad to worse SCART -> Svideo adapter from Amigamaniac -> Indi ECS. If I had to choose the cheapest and best option it was the Svideo adapter + Svideo to HDMI adapter.
Best solution not including price, Indi ECS.
Same situation for the A1200 which I can also use the Svideo adapter. Love the 1080p WB screen with the Indi Mkii.
As for other consoles, my DC has a VGA adapter box. The Master system has been modded with onboard component and other interesting mods etc etc....