Which would get me more money parting out my 1994 mustang gt or selling it all together?
Depends. If it was a 5.0 and is in half way decent shape you might get a little more out of it since there are enthusiasts who still buy these and and restore them. If it was wrecked badly you will probably make more by scrapping it.
A decent 5.0 engine could get you 250+ and pair with the transmission might get you 500+.
Your looking at a lot of work to part one out but if you pull every good part you can find and put it on ebay you might make something, but it would be over time and not all at once.