in the same rod length why would you want one vs the other?

Extra fast for baits with single hooks.

i like XF for dedicated bottom bait rods.

F is a great all-around action: bottom baits, spinnerbaits, smaller cranks. i can usually cast further on a F action rod.

I dont like XF for anything. Its just about what you prefer.

I have a 7' MXF baitcasting rod that is my favorite. It has a soft tip that loads quickly with plenty of backbone for bigger fish. It works great for a variety of baits. I use it most often with light Trigs and jigs.

I personally like F vs XF.  I feel like it casts better, but that is just for me. 

A slower tip will cast farther and wont be very soft, while a faster tip will be softer, but wont cast so far.

For single hooks I like XF

For REALLY BIG single hooks I like F

And for cranks- depending on depth- I like M - MF - F