Hiya,
I did a lot of experimenting at first, and found the best way for me to get good quality on YouTube (starting with a FRAPS recorded .AVI file) was to export into the .FLV format.
I use Adobe Premiere...my workflow is pretty simple, chuck the FRAPS footage (made either from AH film clips, or recorded directly in game) into Premiere, edit as needed, export media as .FLV
My YouTube channel is coombzy283, there are a bunch of vids up there of various games including AH so you can see the kind of quality that you can achieve with this method. You just need to select one of the higher resolution options once you have started loading the YouTube clip.
http://www.youtube.com/watch?v=ISviFJZks_8Unfortunately I believe Premiere is quite pricey (if you actually pay for it).
edit: after looking at your linked YouTube clip, your quality seems about right. You just have to click the cog in the bottom right of the window and select 1080p.