It's thuh, unless you are emphasising that the thing you are talking about is the only or preeminent of its kind.
Unless you're from where I'm from, where it is 'ee', as in:
"ee fills ee shotgun cartridges wi' ee carraway seed, puts ee cheese on ee back step and gie's it baith barrels o' ee twel' bore. Not only does 'is gie us ee even distribution o' ee carraway seed through ee cheese, it also has ee advantage o gettin rid o' all ee magguts"