What can I say... hmmm... you're weird? I do not enjoy having things in my ears clogging it all up so I would have to pick oral sex. It just seems having something in my mouth is much more enjoyable than something in my ear.
You probably mean the other definition of aural sex: "The act of giving or receiving mental sexual stimulation with or from an especially pleasant voice and/or accent." Why pick one? I pick both! Variety is the spice of life and sex. Enjoy it and be safe kids. And always wear protection, that means some ear condoms if you are practicing aural sex.