Medium rare keeps me happy in general. Not too bloody, not too tough. The outside absorbs just enough of whatever you decide to put on it, if you decide to put anything on it.
This is assuming it's at some decent restaurant, like a non-chain italian restaurant or something. (Or a Basque restaurant in Elko... mmmmmm) If it's a breakfast steak from the Casino I go Well Done. (Like they give me a choice) In general the better the quality of the steak, the closer to Rare I go.
Of course I'll eat cuts of beef mildly seared -- like beyond Very Rare -- or raw with the right seasoning. Gored Gored: Ethiopian dish with tasty spicy sauce goodness and seared beef. Very tasty.