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.
Be fair now, it does a lot of useful things and there are a lot of replacements being build right now. Yeah sure, it doesn't do the the useful things very efficient but guess what? You got to row with paddles you have.
Stop complaining and start doing something productive for the OS community if it is so dear to you.
Name ONE useful thing that it does.
I dare you.
Fact is that it doesn't do a SINGLE USEFUL THING.
It is pointless bloat.
the new html5 player works great, but you dont have the option for hd videos plus at random times you will still get the old or the new flashplayer and not the html5 one.
Contrary to the "new video" feature of html5, you DO NOT NEED html5 to embed video directly in web pages. You just need to throw your video into an <embed> tag and its done! ANY sensible browser with a video player plugin will be happy with that!