They are basically the same thing but for the clearly superior tahini sauce the Arabs use over the tzatziki used by the Greeks. What do you call it and eat more often?

Well, as there arent really any Greek kosher restaurants and tzatziki is dairy based so out for me, this was an easy answer, schwarma (of the Israeli variety not the Arab variety)

The spicing of the meat is different between the 2.

But a good homemade tzatziki sauce is such a delight! We make a big bunch and use it as a mother sauce for a whole week of greek cooking. Tzatziki on gyros and souvlakis, tzatziki mixed with some avgelomeno over dolmathes. Tzatziki on a mezze platter with pita, tapenade, and roasted pepper and basil hummus. Any leftover tzatziki can be thrown into a vinaigrette for a week or so to jazz it up.

If anyone wants a good tzatziki recipe, let me know!

Where I live now I have yet to find a decent gyro. (Palm Beach isn't exactly renowned for ethnic food besides French and Italian). The shawarmas I have eaten around here all seem to be chicken-based, not beef/lamb based.

In DC, when I was in school there was a place called Fast Fetoosh in Georgetown that had what I considered to be the world's best gyros (my opinion may have been affected by the vast quantities of beer I usually drank before going out for gyros at 2 in the morning).

You obviously need to come further South Rothko

You are correct.