I'm tempted to say neither. In fact I do. Don't do either of those two methods.
Designing, writing, testing and using your very own yet another templating system is hugely inefficient. Likewise doing the same with formats doesn't help a lot either.
If you need things to go fast perhaps you should look at CGI::Fast or mod_perl. That'll cut down the execution time a lot.
Back to the question at hand, however. I would recommend the good practice of using someone else's already well designed, written and tested templating system. For example HTML::Template or Template::Toolkit depending on which one best suits your needs.
Formats are almost a thing of the past (thankfully) and I can say with certainty that you'll appreciate the joys of using templates, sooner or later. You want to use templates, it's a good habit to get into for when you later have to share a project with a graphic designer.
Hope this helps,
In reply to Re: Efficiency/Speed question... (files or formats?)