I can only recommend a main dash based on my own experience and requirements. Having said that nobody worth listening to could argue against XBMC as it is the most sophisticated by a country mile. If you're wanting to use the Xbox for any multi-media stuff, TV, pictures, video, music etc then there's no other dash like it.
However just for gaming UnleashX (v.572*) is still the dash of choice for many people. Think of it being like an enhanced version of the MS dash with almost all the things you could possibly require to customise it. The File Explorer in particular has a GUI second to none in function and design, featuring an inbuilt text editor and virtual keyboard which can be very helpful. XBMC's File Manager won't, at least none of the versions I've used, even display text documents.
UnleashX's music player is crude in comparison to XBMC and has more than a few flaws but it works OK.
Avalaunch and Evox etc are considered a bit old and under featured now but have certain capabilities which can still be useful.
Whatever main dash you go for always install another or indeed all the others as Apps.
* I suggest UnleashX v.572, if you can find it, rather than the last released version v.584. The latter is otherwise fine but has a fault in the Games Saves Manager. For some reason it won't dsplay the individual save files on any attached memory card/memory device.