USB Loader GX, currently at r938.
Personally I've read a lot of negative posts about USB Loader GX, but most of it is due to user error. If you stick with the non-beta versions you won't have much drama using it. If you use the beta versions, well you should know what you are getting into. I use the beta versions, and knowing so, I take precautions, and read the change-logs.
That said, comparatively, USB Loader GX isn't on the bleeding edge as far as new features go or updates for that matter. Other USB Loaders seem to be updated more often, and with fewer bugs in comparison, from what I read.
USB Loader GX continues to work out for me without ever having a major issue where I could not play a game. Nice, simple, and looks good.
-[]D