I feel that there is still a massive need for both. I am 100% a developer. I'm horrible at front-end design. (It took me 40-50 minutes just to properly align, code the CSS, and restructure HTML to display 3 extra "social" buttons on my site.) Give me a good project in PHP and I'm in. However, both skill sets have a need in the industry. @SnOrfus already said this.
My advice is to go with what you are good at, but understand and know the basics of the "other" side if possible. And as you learn more, you can better decide where "more money" is based for yourself. If you happen to get a job as I have, where you alone are responsible for maintaining the front end and back end, you'll most definitely have to learn both.
Front end will not survive with out back end, and back end (PHP, etc.) will not survive without front end. They go hand in hand.