Use the best tool for the job which you're comfortable with.
If you prefer Python over PHP, then go with Python. At the very least you'll be comfortable with the language you're working with.
A friend of mine recently tried to convince me that Erlang is the way forward for the web. I scoffed, until I saw what kind of performance they're getting on a slightly older server with a bunch of Erlang-powered sites running on it. We're talking orders of magnitude faster than any other language I've ever used (or heard about). I was very, very impressed (and envious: "my stuff doesn't do that!").
Remember, a couple of years ago everyone was talking about how Ruby (and especially Rails) was going to 'kill' PHP. Didn't really happen, did it?
Yet I'm sticking with my PHP. It's what I know, it's what I'm comfortable with, it's not going away soon (never mind what others might think, it's still the most used server-side language on the web, and the language is evolving and maturing at an incredible rate) and there's enough there for me to continue learning and improving my skills.
To sum up: choose what you feel comfortable with, not just the cool new kid on the block (just because it's the new kid) or the established, venerable language that everyone else uses (just because everyone else uses it).
Wow, I wrote a whole post without a single smiley!