Depends upon the model and the pilot. If you are the type who tends to bang the sticks then low/high rates would be a better solution.

I don't put exponential on trainers (you want to "feel" the same control throw throughout when learning) but a sport model might benefit from 20%. A 3-D model maybe 60%. That's what I have on my Hot Stik.

Better to use low and high rates of 15 or 20% difference. Set the high rates to 100% throws and drop the low rates by 15 to 20%. My Futaba 9C allows me to use low rates without exponential and high rates with exponential. That's generally how I set up my sport models, but I go to as large a throw as I can work out on high rates rather than the recommended high rate. Then, depending how it flies, I'll tone it down with the servo end point/volume. And that, again, is a personal style choice for how you like a model to fly.