First off I don't really like to go with extra apps on my Mac. So with Leopard I'd use (mark's) PHP (as 10.5.x didn't have GD support at least) and official MySQL distribution. With Snow Leopard (OS X 10.6) Apple did a great job rolling out quite a nice http server but to the date it's way too advanced for my normal dev life. None of the web apps I do develop with (Druapl, ExpressionEngine, Joomla, WP ... ) are ready for PHP 5.3 yet. So the only choice was downgrade.
I've tried a few ways as MacProts, compiling my own PHP (and libs) but that was not even 90% successful or buggy. So I looked to MAMP again. Here are a few tips to get MAMP running nicely at OS X 10.6 (Snow Leopard):