Neither. What does your app need to be able to do? Make sure the hot valve delivers hot water, the cold valve delivers cold water, that the water flows in the first place, that you can extend pipes wherever needed and then worry about implementing actual plumbing to all rooms of the house or what the house will actually look like exactly.
The front end is just a mask with some switches and levers on it. The back end is just a thing that receives requests to retrieve and process data. Get to a point where you can rapidly implement both in any desired combination first.
But whatever you do, don't let the design of one dictate the design of the other. That way madness lies.
Get the tools in place to let your devs build whatever the heck they need for your client, regardless of how many times they change their mind. Then build it to specifications and rejigger it until the little cusses are finally happy.
Also, comparing front end devs to back end devs in 2008 is a long time ago in web years. For the sake of fun, I'd like to correct/add a few things to that old chestnut since we've linked it in the question, but also (hopefully) embed a few tips within:
Front end developers
Typically don’t have a CS degree, or have a CS degree from a 3rd tier school.
Show of hands. How many people with CS degrees have been taught best practices on the front end? Or how to not make a mess with JavaScript? Or how to handle CSS problems from IE6-IE9? The textbook industry, which runs academia, is too fat lazy and bloated to handle constantly shifting technology so it has received very little 'serious' attention in colleges. This has been excellent for late-bloomers like myself.
Work in languages that similar to basic (see PHP is Basic)
Because PHP is client-side technology? Or because JavaScript, which was inspired primarily by Scheme has more in common with Basic then Visual Basic which is now no longer a going concern on the front end and never really was but is still available for back end .NET web applications? The blog compares self-taught open source web developers with CS grad web developers using corporate-popular tech at this point I think. I've run into insufferable and competent in equal shares on both sides of that particular fight but he's still way OT there.
Have a visual skill in converting photoshop documents to CSS/HTML/etc.
More attention to detail than "visual skill" which is a bit broad. Not all of us have any aesthetic design skills whatsoever. But yes, most of us have to learn this stuff at the Jr. level and it's actually quite thoroughly critical to writing good UI that doesn't use JS hammers when CSS scalpels will do.
Have a high tolerance for iterative programming, due to type free languages
This is why you want the pieces I mentioned earlier in place first. We pass on the buttons pressed, you produce/retrieve the goods. We package and deliver them. There is no reason for these things to in any way be tightly bound to each other. Also really, strict typing should not interfere with an iterative process if you don't suck at OOP which most people who like to get haughty about a language not technically having classes, in fact do, typically. But even if they do stink, the front end only needs a predictable point of access and you can do whatever the heck you want on the back end as long as you don't do something silly like dynamically write JavaScript that isn't JSON or tightly bind successful back end behavior to HTML structure being "just so." *cough* java devs */cough*