My choice of boat is an IX. There's several reasons for this:
-ability to see exotic places. I love the Caribbean!
-a lot of torpedoes. In my current career I played IX until early 1944, and never had problems with external torpedo loading. It's safe.
- heavy flak arnament. I'm playing GWX 1.03, and with the 2 cm vierling and two dual 2 cm guns I usually shoot down any aircraft that comes into my way. Haven't lost a single crewmember yet, because the planes will be shot down before they release their bombs
- no problems with port raiding. Even if the boat is big, it's very possible to sneak undetected to harbors. During the last five patrols I have raided the ports of Guantanamo Bay, San Juan (score: two large tankers and a liner
) Santo Domingo, S.t Helena (score: two cruisers, medium liner, large tanker, large cargo and a fishing boat), Cape Town and Bridgetown.
So my message is: Don't be afraid of IX even if the boat is big. It's the boat of success!