I like the low/narrow, but I make smaller instruments. I started with the medium and migrated down.
The great thing about Gitty is you can get small quantities for just a build or two and try them on for size.
Justin - as Mark said, medium/medium is pretty much the perfect size for a standard guitar.
Here is a link to mine. If you find it cheaper anywhere, I'd like to know about it! http://www.cbgitty.com/cubecart/index.php?act=viewProd&productI...