Well normal busybox is good enough. But you have to compile it yourself. The Sarge verion and the emdebian binary package don't need to be compiled anymore and are known to work. This saves you a lot of hassle if you are not used to it.
busybox is by it's very nature something that you would want to recompile to make sure you have only those things that you need, no?
I think a good embedded system based on Debian would take this need to recompile into account. From the web site and docs, I don't really know what emdebian does, if anything.
-- David N. Welton davidw@eidetix.com