I don't have experience with Vimscript, but I know both Lua and Python. It seems that the biggest benefit is gained by stepping up from Vimscript to any of thos

I don't have experience with Vimscript, but I know both Lua and Python. It seems that the biggest benefit is gained by stepping up from Vimscript to any of those two. Switching to the other would only have diminishing returns, if at all. Apart from that, Lua was explicitly designed to be embedded. Python is designed as a scripting language that can bind to C code, and embedding seems to be an afterthought.