well as im english i would say Tie-dus and that is how i have heard everyone say his name. however the voice actor James Arnold taylor who does his voice calls him tee-dus

to prove this an interview with James Arnold taylor

http://www.square-enix-usa.com/games...tg/taylor.html

however this would not stop me from calling him tie-dus i think that where your from counts for different pronucations, and Tee-dus is the american way.