"lowest score" would be self explanatory. "Best score" still made me think I was doing better with a higher score
on the other hand, it might be better to change the scoring system. Calculate the worst score using the current system. Then reverse so the score goes up as in displayScore = worstScore - oldWayOfCalculatingScore
edit: managed to get a score of 131 for getting to 0 fragmentation in 30 seconds, i had 139 from just spamming space