This year will be my first to butcher turkeys too so I won't have a taste comparison. My turkeys run with my chickens and ducks and I feed the whole flock a balanced grower/finisher formula. They also have range of 10 acres and over the summer we had a grasshopper infestation and the turkeys were more than happy to help us out with it. In addition I've watched them eat a ton of grass and other greens they find growing.
Cracked corn doesn't have a lot of nutritional value and as we go into winter it is harder for them to find what they need while ranging, so you might want to finish them out on some variety of "finisher" feed that you can find at your local feed store. For example, the Purina brand is called "Flock Raiser" and Nutrena is called "All Flock". Each region and store has its own offerings so I would just look for feed labeled "grower" or "finisher" preferably with a protein content of 18% or greater.