I've done both. Found Keto is great if you're planning a long less intense ride. But for fast attacks - recovery - then attack again, keto just won't do the trick over the course of a 1-2hr race ( I suspect the same is true for any race that features surging). I found I had no energy left after attacking only a few times. That being said - Keto is an easier diet to maintain once you've switched your eating pattern to match what is required to remain in ketosis - that is to say you don't have to worry so much about fueling for the ride as you probably constantly have an excess amount of body fat to fuel the ride. Carb diet does give that missing power/recovery ability that is missing from the keto diet. I've switched back and definitely see better results.
What would be an interesting experiment is practising a keto diet and only consuming enough fast-digesting carbs to fuel for the ride itself. Maybe it would result in burning fat for lower intensity and tapping into glycogen when the body needs it for higher intensity - whether or not that is possible is beyond my understanding.