I'm the author, let me just answer this one. Spirit produces recursive descent parser, ctpg produces LR(1). So the parse speed is just much better. And the set

I'm the author, let me just answer this one. Spirit produces recursive descent parser, ctpg produces LR(1). So the parse speed is just much better. And the set of possible language grammars is bigger. Plus (this is just my opinion) ctpg just looks more intuitive.