I don't like Litphoria's way, because I select Mandatory, Core, Yes, Will_Try, or No first. I have to go through the entire list of interests FIVE times, once for each category, which is exhausting... Or I can take a mental note of the interest, scroll way down, select the desired list, scroll back up and find that same interest again, then click it. I find that even more exhausting.
I like F-list's way, because I can go through their entire list of kinks once. For each kink, I select Favorite, Yes, Maybe, or No. Makes sense, even if the interface is messy looking.
The first idea that comes to mind, is to make it so that when you click an interest, a little popup window appears under your mouse cursor. Add interest to: Mandatory, Core, Yes, Will_Try, or No. A little X button to cancel out. That way, it does it the good way, but is cleaner looking.