If I had to choose between those in the poll, I guess Thee-uh-derr is the closest. What it actually sounds like to me is Thee-aæ-r(e)r. The a is based on the typical European pronunciation of the letter and the æ is Norwegian. The first r is a Norwegian/Spanish/whatever r without the rolling, and the last one is the potato sounding American one. The e isn't really there.
That sounded complex. Well, I guess it had to be since English is a "non phonetic" language. For the record, what I described is what I'd say is the American way of pronouncing it.