For track, assuming elevation changes, curbs and bumps, the Normal setting gives the best all around result, because it stays active and can actually adjust harder than the Sport setting, if called for. At the Advanced M-school last week we were told to start with Normal and experiment. When it rained, the Comfort mode gave the best result.
I haven't tried it yet, but I think that Sport may be best on a smooth autocross course. At VIR, the Normal was excellent, particularly for those using the curbs on the esses. Also, braking from 140 or 150, we got better weight transer and improved braking at the ends of fast straights. I tried the Sport a couple of laps and noticed a sizeable drop in braking performance as less security on the uphill esses, where you need all the security that you can muster.
So, it's track and weather dependent. Start with Normal and adjust to circumstances and your personal driving style.