I haven't personally run all these options but I'll just share my understanding of the relative strengths of the video types:

Composite vs. RGB vs. S-Video vs. Component vs. HDMI vs. RF vs. VGA

Composite (assuming three-plug stereo RCA or RF) - easy and cheap video capture but poorer quality
RGB - good video capture options but expensive, cables required, mods often also; some confusion due to various scan rates (15KHz for classic arcade and some consoles / computers i.e. X68000 / FM Towns; 24KHz for "medium resolution" such as the Sega System 24 (Crack Down, Scramble Spirits); 31KHz also (VGA runs at this scan rate).
S-Video - good balance between ease of capture, good audio sync options (afaik), and good quality; good support among legacy consumer systems
Component - good picture, ease of video capture, more expensive
HDMI - good picture quality, some reasonable video capture options. Downside: many sources (i.e. the PS3) disallow capture via HDCP.
VGA - actually a form of analog video more or less similar to RGB. Good picture quality up to a certain rate, still one of the most cost-effective ways to get high resolutions due to ubiquitous hardware. Cons - no audio information sync, video (or even stills) capture is expensive. Similarly look at DVI, which seems to already be at the end of its short life.