Base it on your preferences. I tried already lua and prefer it. Angel script may be a bit easier to debug while lua has real coroutines and I think is faster (especially last lua release).
There are out there lua editors for sure, don't know about angel script.)
also consider dependencies, if you want to use lua, you want for sure to use also an additional C++ framework to automate most binding tasks, while angelscript have that feature natively
also note that based on my experience Angel script is not a full fledged OO language so if you are used to stress limits of the languages you use (in example you go heavily with templates and reflection in C# and metaprogramming in C++) then probably you will find better with lua because thanks to its "dynamicity" allow to overcome the limits of the language. Said that, you have to try both.
I think I'll try Angelscript now, I just saw it has Cmake script => easy compilation