Trying to decide between custom post type and custom field

Our current sites, the ones we're migrating to WP, have three types of information: pages, articles, and news. Pages map easily to pages and serve the same purpose. News items map easily to posts. But articles are, well, articles and they're more complex posts.

We display articles and news in different loops on different pages. So, right now, I'm trying to decide whether to create a News Item and Article custom post type, or just add a custom field in Posts to differentiate between 'news' and 'article' for the purposes of where they display.

Any thoughts on which approach is better?

Thanks!