Well, it's at least a lot more complete.
So rather than doing your flamewars, has anybody actually tried that thing (I know, crazy idea...).
From the writeup, it looks like Gnash is "mostly complete" for ActionScript 2, with no real ActionScript 3 support. LightSpark is "mostly complete" for ActionScript 3, but does not handle previous versions at all.
This would make it very difficult to compare the two for performance or compatibility, as no SWF files would even try to run under both of them.
AVC is merely another name for h.264. AVC is the name used by the MPEG consortium, while h.264 is the name for the same thing by ITU-T.
The 3GP container format is an implementation of MPEG-4 Part 12.
3GP uses AVC and AAC.
GNOME-MPlayer fills the buffer first which is set to 2MB by default. You can decrease the buffer size to achieve immediate playback.