which is more effiecient and fast doc() or collection(

Working on converting an XSD to SVG (will hopefully look like TURBOXML's lovely
view). I'm mainly using doc() with a regex to parse the various directories of
XSD files. Since the XSD is built modularly and each element in its own file (I
personally do not like reading XSDs or XSLTs (for that matter) in one large file
and have to scroll up and down to make sense of it all, but that is another
discussion) meaning there are a lot of files. So before I test it out and spend
time on switching from doc() to collection() I was hoping for some feedback. 

Which is the better method? Which is faster or more efficient?

Marijan (Mario) Madunic