When I went shopping for a trans, my choices boiled down to two. B-W T5-Z, or Tremec 3550. Both involved compromises, and neither was the best solution for everyone.
Tremec has a web site that explains the differences between the two.
Since this has been discussed at length here, long story short.
After a rather lengthly conversation with Liberty Transmissions, I opted for the close ratio (2.95 1st) T5-Z, blueprinted, and with the .62 5th gear swapped out for a .80. Filled with
synthetic ATF, and topped with a Hurst shifter, I have a trans with 5 useable gears, and a 2300 RPM cruise. Shifting is quick, and smooth. With now 16,000 miles on it, have had no service problems, and don't expect any.
Today, were I to put a Honker motor in the car, and get on it a lot, I'd get the Tremec T-600 road racing trans with 2.87 1st, and .82 5th. It uses a different bellhousing than the T5, different driveshaft yoke, and the length is a little different. But for sports car style driving, the smooth and quick shifting close ratio T5-Z is hard to beat.