I am not an expert in regards to FORTH so I'd have to let someone with more experience say. FORTH from what I know has been around since at least the Z80 days. But honestly, I do not know if it carries more or less baggage, nor whether it is really more portable.

All the embedded work I have done has mostly been C with a little more C++ in the recent years, outside of some machine level stuff for highly specialized devices. So just from that, at least in my experience C is the more common, portable and easily worked with language.