Louis and Jenny sing ___ （beautiful） at the singing competition 用beautifully的原级还是最高级

语法上,两个都是可以的,具体用哪个要看上下文.比如：1) Among thousands of singers,Louis and Jenny sing the most beautifully at the singing competition,so they have won the first prize.
2) Louis and Jenny sing beautifully at the singing competition,thanks to their beautiful voice and great effort.