UnleashX by a landslide.
Evox is, for the most part, outdated. i only use it when repairing TSOP mods, to flash the bios. i can do that with another tool, so that's not a big deal. Some use Evox for trainers, but those are in XBMC now, so again, not needed.
AvaLaunch felt okay at first, but it screams if you use a ShadowC drive system and a chip at the same time....it also freezes a lot for me doing the things i kept it around for, so besides the shoutcast streams, this one is useless to me
as for XBMC, the XBMC team has stated that programs/apps in XBMC was a tacked on feature. Also, though its being updated still, the amount of crashing/bugs/upgrading that has to happen over time makes it less appealing as an actual dash and more as just an application....
UnleashX sometimes crashes on me, but very rarely. XBMC crashes if i do too much at once.
in UnleashX you can do all the virtual file folders you need to, and organize things the way you want, where as in XBMC, last i checked, they didn't give you much choice as far as order or organization goes.
Lastly, unleashx is REALLY versitile....built in file manager, built in media player for mp3, wma, wmv, xbx, jpg and xmv. built in zip file support. animated skins with a simple skinning engine, scripting/batch commands....enough stuff that you can create a Log In screen and set up profiles if you want to. I used UnleashX in a similar way to Guybird's, as a front end for a personal XMugen project, but i was able to create me own animated skin, automate several things such as resolution, clearing of cache, and eventually, controller type. it really was a fun time for me for a little while