1.4b is the best and most recent patch:
http://www.silent-hunteriii.com/uk/updates.php
Make sure that you download the correct DVD patch, there are two different versions. When you install it it says v1.3, but that is just a small bug.
The best all-in-one mod is "Improved U-Boat", you can download it here:
http://u-boot.realsimulation.com/