I believe most code uses the same methods as japhy's example above. I know I've never used the (..., undef, ...) method, but I have used the (...)[0,1,4] method many times. Granted, my experience doesn't include everyone, but I don't recall seeing the undef example in any Perl documentation, while japhy's example (if I recall correctly) is shown.

However, as always it's just a personal opinion. :)