I...don't...know...
There are some sources I do enjoy editing with (Mushi-shi, 5 Centimeters Per Second) but there are quite a few other sources I'd love to edit with and just never had a concept for. Honestly, I don't think I have any source that I can't live without.
Evangelion, series, End of Evangelion and the rebuilds, I didn't earn the nickname Evawhore for no reason.
Maybe some FF7, since it's my favorite game, in movie form, cannot go wrong with favoritism.