Most popular wedge shaft on tour is Dynamic Gold Tour Issue S400. Good place to start.

Honestly comes down to your ability and what you are looking for. I played in college and scratch still today using S200 for the feel on my high lofted wedges. 54-58 since most shots will be 3/4 to pitch. Going with too stiff of a shaft on half wedge shots can be miss leading.

Full swing wedges like 46-52* are at S400 but again it's all in how you play your wedges and the feel/kick your looking for.

Stock Wedges will come with S200 shafts
Honestly wedges are the biggest "art" of golf and really comes down to how your game is crafted from 135 and in.
I'd recommend a wedge fitting and gap analysis with a local Titleist rep they'll be able to dial you in.

Good Luck!