Versatile Length for a Kayak

What length kayak in your opinion would be the most versatile for all fishing situations?

12 to 13 feet. Having said that, I own 4 kayaks and none of them are under 13 feet.

12' without question!

You can get by in fast moving rivers, large lakes, or offshore. Manuverability, fairly decent speed depending on the kayak model.
An all around most versatile that would get my vote would be something like a Tarpon 120 by Wilderness Systems.

yep!