Note that Method #2 is buggy. You will not grab the argument, but the length of the argument array. You mean

sub myFunction
{
     my ($arg) = @_;
     #blah blah blah, do some stuff.....
}
myFunction($myArg);
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so that the assignment is in list context. See Context in perldata.

For my own work, I usually use

sub myFunction
{
     my ($arg1, $arg2, ..., $argN) = @_;
     #blah blah blah, do some stuff.....
}
myFunction($myArg);
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unless I'm writing an object method, in which case I use shift to get the reference:

sub myFunction
{
     my $self = shift;
     my ($arg1, $arg2, ..., $argN) = @_;
     #blah blah blah, do some stuff.....
}
myFunction($myArg);
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though, if it's just a quick and dirty iterator over a list, sometimes I skip stripping the argument array entirely:

sub myFunction
{
     for (@_) {
          ... # lvalue; Note this impacts the passed values!!
     }
}
myFunction($myArg);
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See also Best Practices(TM) reference card, noting that it doesn't weigh in.