Scart is the proper way to get a decent quality. Don't expect miracles though because amiga chips and games are not designed for LCD screens i.e some transparencies in some games are dithered gfx and don't look proper on lcd. Also there is some interlace flickering at color cycling/blinking (like the tail fire on DGalaga)
But in the end the picture is fine and that depends on your TV's upscaller too.
Caution, do not use any of the old scarts, they will propably blinking and if they are not they may damage your scart circuit from the voltage. You need one SCART* with resistors.
As for capturing use the composite outpout, Youtube has not the best video out there and the framerate is low.
On the Amiga 500 you can use a scart for color output with an old vcr and if this has a second scart you can drive its output to your capture device with a scart to composite cable. The TV Modulator suxxxx.
*This is a preview of the scart I built :
http://youtu.be/AHJ1aYEHs1U?t=32sKatalaves?
