Depends on the competition: 1) for shorter, intense events, such as triathlons I go for digestability and high energy content, with some protein bundled in for muscle protection only. 2) during multi-day ultras, I try to get as many calories in as there is no way of replacing every one lost – a daily deficit is part of the deal. So, running through different types seems to work for me, aiming to get as much as possible in paralell, as frequent as digestible and with different absorption speeds: complex carbs, simple carbs and fat. An eat fest!