As has been said before, a TFT output looks best with a signal in its native resolution or a multiple of it.
An SXGA (17 or 19") TFT should look OK with the Amiga's somewhat VGA output (at least in PAL) - as long as the monitor can cope with the low vertical scan rate. I'm quite satisfied with the output quality of my Merlin RTG in 800x600 on my 19" Samsung. PAL flicker fixed (A3000) looks pretty nice, too.
I did have to adjust the monitor quite a bit though, auto settings didn't work at all due to the exotic timing. To get the best output possible: Disable all overscan. Display some text, some diagonal lines and a fine checkerboard pattern or vertical lines, everything in full width if possible. Then adjust the 'clock' until the vertical bands get as broad as possible. Finally change 'phase' to gain sharpness.
