I think what it boils down to is that if you are happy and enjoy the Type II, then use it. I was, and am, a big fan of the Type II...you really are getting to learn the finer points of the game as well as bonding with your crew.
In my personal experience, I have found that the Type IVB is the boat for me...that thing is sturdy as all get out, and I love it. I have taken it, literally, to the bottom of the ocean and back!