Personally ...

I find that XS makes faster code, since it does not insert another layer of abstraction like SWIG. I think that XS is the best long term solution, since it is the interface provided with perl, and creates very tightly integrated code (letting you handle argument stacks and such as needed). But, i have to admit, porting large libraries can be tedious (but worth it in my opinion)

When i have used SWIG, i have found that quite often it creates code with minor problems that have to be fixed to get it to compile. Since SWIG creates an entire abstraction layer, this C-diving is not simple. But, if the code it creates works, it is ver fast to impliment.

For me, SWIG is quicker to create code, but XS creates better code. Your milage may vary.