You need 800x600 in order to include the full overscan output area of an Amiga don’t you? If not, games like Pacmania will have some of the display missing.
Problem with scanlines is they look horrible on 17” or larger monitors. On 15”, they are acceptable and nostalgic but most people have larger displays now.
So it’d be 800x600 16bit, full screen, doubled, no scanlines, directx/opengl centring, no LEDS.
Best resolution is a non-standard res somewhere in the 700’s area as it has the required output size and is fairly well centred without using other options. My Geforce2 used to offer this resolution and it was ideal. This resolution isn’t standard on ATI cards however and has to be added by the user so you can’t use it on the DVD.
If you don’t want to include directx/opengl settings in case of compatibility issues, then you can perhaps use the “centering options”. They used to leave a black box on the right hand side in 0822R7. Not sure if this has been fixed in later versions?