I've worked with both PHP and ColdFusion for years, and actually like both of them.
There are at least five things to think about when deciding which technology you should go with:
Your monetary budget
Your development time budget
Your support needs
Your server specs
Your application needs
ColdFusion costs money up front and with every upgrade. PHP is free.
You can get a site up and running in ColdFusion in 10 seconds flat. PHP generally takes more time because its syntax is pickier and requires more of a programming bent.
This site notwithstanding, ColdFusion user community support is generally a lot more limited than PHP user support. I suspect that it's because people figure that if you can afford to install ColdFusion, you should be willing to pay for support.
ColdFusion runs as its own engine, on top of the web server application. PHP can run as a CGI, or as an Apache module. This definitely has an effect on website performance, though your mileage may vary, depending on what kinds of things you're doing on your website.
PHP has over 700 built-in functions. This is amazingly beautiful and terrifying at the same time, if you're a brand new PHP user. PHP has extremely cool file-handling functions and can run circles around ColdFusion in just about every arena of functionality - database connectivity, interface logic, you name it.
And it's open source, so you see new, cool, FREE stuff getting added on all the time. A friend of mine wrote Ming, a Shockwave Flash generator plug-in for PHP, and now it comes with the standard install. How totally rad is that?
The real challenge is accepting that there is basically nothing you can't do with PHP, and also accepting that finding the function(s) that does/do it may take some time.
I hated ColdFusion at first because it seemed very...clunky. As Duplo blocks are to Legos, ColdFusion is to PHP. You know, like with Duplo blocks, you can build a house, but it still looks like a big block, whereas with Legos, you can build a house, with turrets, witches' caps, a palm tree in the front yard, and even a little clawfoot tub in the Lego Bathroom, if you want. I have a friend that used to call ColdFusion the "Fischer-Price My First Programming Language."
But I still have a soft spot in my heart for ColdFusion, because I have been able to get Duplo-style sites up in no time with it, and I just KNOW that creating the same functionality in PHP would take a lot more work.
So: lazy? rich? not afraid to limit your functionality? go ColdFusion.
broke? creative? PHP, baby, PHP all the way.