I use FBA-XXX for arcade games I see no reason to change it plays everything I want without any difficulties.
xbox-scene is the place to go for information. xbins on efnet (IRC) is the place to go for pre-compiled emulators/dashboards/apps (it's illegal to compile and distribute xbox software due to the licence on the xbox dev kit. So it's very rare to find emulators compiled in the wild, IE web pages).
If joining an IRC server to gain membership to the xbins FTP is too challenging then bitgamer is definitely the place to go for computer noobs (I don't mean this in a derogatory sense) everything is compiled and in nice packs where you simply either transfer to the xbox or burn to a dvd.
If you need a bitgamer invite I can give you one.
Edit: Found the guide for getting on xbins with mirc. Dead easy.
http://www.xbox-scene.com/articles/xbins.phpI prefer the xbins route because I get to choose exactly what I want on my xbox, Sometimes you don't need 100 and 1 versions of street fighter to play street fighter y'know?
Regarding dashboards, I prefer unleashx, I've tried em all and the most customizable and easy to use is unleashx, the skins are editable really easy (just xml files) if you can code a webpage in html/css you can edit the unleashx dash. I have mine so that I have XBMC as the first option, then options for Games -> list of games, Emulators -> list of systems with proper system icons made by me, Apps -> list of apps, Utilities -> options, shutdown, msdash, etc. Really clean and easy to use.
XBMC just has too much extra stuff for me as a main dashboard, I like to have it there when I need it, but I couldn't use it all the time, plus unleashx loads instantly, xbmc takes about 10-15 seconds to boot up depending on the theme.