It's a matter of personal preference.
Some people say PHP is bad because it doesn't have a very strict syntax and you don't have to declare variables.
In Java the compiler will beat you if you don't declare a var, or if you want to put a string into an integer.
Personally I feel it's the programmers job to write code that works, not code that needs to be analysed by a compiler to filter out all the mistakes the programmer made.
As for speed I think PHP and Servlets are close competitors.
Ofcourse, it depends on what you make your program do.
In the end, both languages use the same computer, so they can do 99.9% the same operations.
My personal preference is for PHP, because it's so easy to put PHP inside HTML documents and edit them on the fly,
whereas Servlets need to be compiled before they can work.