Embedded scripting languages

What scripting language would you embed to a program? The performance would not be main issue, since the compiled part of the program would worry about that.

The scripting language would call many functions written in C, C++, or whatever lang that can compile C-like functions (so there needs to be some kind of easy to use FFI).

I thought about options here:
- Lua
- Scheme (tinyscheme or whatever)
- Something else?

Now, what would /prog/ use, and why? ("Read SICP" is not a valid answer here)

How do you implement an object-oriented programming language without representing the objects as hash tables? For it to be truly OO, you need to be able to add and remove arbitrary object fields during runtime, so the interpreter/runtime/VM needs to use some sort of dynamic representation for them. Or do you just analyze the AST to determine that a certain prototype chain only ever has certain certain fields, and then translate them into memory offsets?