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.
Work in languages that similar to basic (see PHP is Basic)
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