I'm not sure if I'm on time here...
While I have not had too many meals at Costa's, of the places I have tried in Greektown, it is one of my least favorites. I would also add that while I like Santorini a lot, and all things being equal, is what I'd call the best of, but it is also the most expensive.
Me, I also like both Parthenon and Pegasus, especially the former. I was just there. The food is a little on the rougher side, but that's one of the things I like about it. Very hammish kinda place. Not the best of pics, but here's what the stuff looks like.
Think Yiddish, Dress British - Advice of Evil Ronnie to me.