Anywhere from Medium Rare to Medium Well is perfect. Steak juices are okay, but it's about the texture that goes best with the seasoning you're using. If you're using steak sauce, you want to get it closer to Medium Well, since the steak sauce will drown out the taste of the juices. However, if you're just searing it in butter or using salt and rub, you want to get it a little rarer, that way you can taste the juice with the seasoning.
The Japanese have wagyu beef, so ultimately they don't need either seasoning or sauce. You cook that sucker rare, with a bit of butter, and it's absolutely delicious. The marbling on it is way better than domestic European or American beef, but it's incredibly expensive, though less so if you live in Japan. They sell 8 oz of wagyu for 3,500 yen, or about $32 for 8 oz of steak, depending on location and season.