My Type IXC, U-527, is going great for me ATM; still won't trade her in for one of those new-fangled IXD2's, regardless of any better capabilities
After 17 patrols with her, I've gotten a bit attached. Sure, I was in U-553 (VIIC) for 22, but since I got U-527, I've been regularly sinking 5-7 ships per patrol
-Qairyl