I might be wrong but I think T-Bones fell out if favour during the whole mad cow disease thing...something to do with the bone marrow.
Personally after many years working in kitchens I don't really have a perfered steak but I do have perfered steaks to use with certian dishes ie
Fillet - I find best cooked very rare with a sauce, as carpaccio or minced down and used in a steak Tarta dish.
Sirloin - Due to this being the 'middle of the range' steak with a good trade off of flavour vs tenderness this tends to be the best steak to use as a 'steak' meal Ie just the steak chips etc
Ribeye - pretty similar to a sirloin but for the people who tend to want a bit of extra flavour. Also ideal to be sliced down and used in stroganoff type dishes, stir frys etc
Rump - Due to the flavour it tended to be the 'sandwich' steak of choice, used in steak and onion baguettes or as a smaller steak choice on a mixed grill.
Again it's a good quality, well hung steak that's cooked right that makes all the difference. Also (and this is just personal choice) I don't believe that anything cooked above medium rare is any good. When taste testing in the kitchens any steak that was well done pretty much Tasted exactly the same as the rest.
If I'm not sure of the quality of the meat I'm eating I'll have a steak medium rare or rare. If its high quality meat then there is no other choice then blue!!