In a recent post from the OnStartups.com blog, there's an article from Dharmesh Shah about why "PHP is fun and easy but Python is marriage material" when it comes to building web-based applications.

So, you might then be wondering, why switch away from PHP and move to Python now? Don’t I have better things to do with my time? [...] Here are some of the tradeoffs (PHP wins on some fronts, Python in others), for those faced with the decision now. Note: The context here is a startup that is a bit further along (HubSpot was 2 years old and had about 50 employees at the time of this decision). But, some of the arguments still apply, even if you’re earlier stage.

They make six different points for you to consider about your application and which language might be the right choice:

• Python is well designed, PHP is not.
• Python has a "clear" web framework winner
• PHP is lingua franca in the world of the web
• Low-End Web Hosting is a non-issue
• Not all Python fans are fad-focused elitists
• Low Learning are less important than high ceilings