I prefer the type VIIB because it can dive faster (life-saving later in the war) and is more maneuverable that an type IX.
Stock SH3 does not reflect the important differences between the VIIb, C, and C/41 - especially diving depth. Besides, the B is marginally faster than the other two variants. That said, you can alter the stock u-boat cfg file(s) to change that to more historical accuracy.........or to build an uber-uboot for arcade play.
If you de-select "limited fuel", you can have the same range as a type IXD2
- just pretend like you are meeting Milch Cows at sea for fuel and food, except that they're fresh out of torpedo reloads when you do. You can sail to the Gulf of Mexico and back and your time on station is limited only by the number of eels and cannon shells aboard.
Historically, the IXs were considered by BdU to be too slow and sluggish for convoy attacks, and relatively easy prey for aircraft and escorts. To overcome this, they were relegated to long-range operations to areas where ASW defenses were weaker and/or most ships sailed solo. This took optimal advantage of their large fuel bunkerage and torpedo load-out.