<STDIN> is fine, what becomes a problem is <>.

use strict; 
use warnings;


while (<>) {
    print;
}
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If you run this with perl -w blah.pl something, <> is going to read from something, and fails if something is not a file etc. This is probably a feature you don't want.

In general, the best practice is to avoid the feature of reading from @ARGV, and in your code use <STDIN>. If you want to have a choice of reading either a file or user input, use redirect.

use strict; 
use warnings;


while (<STDIN>) {
    print;
}
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If you want the input come from a file instead of user, just do something like perl -w blah.pl <somefile.