English Translation
He is one of the best singers of today.
Unnatural word-for-word translation… 立派な歌手 doesn’t mean “good at singing” but is closer to “ethically/socially responsible singer” (e.g. donates money to people in need; brave enough to express his belief, etc.). 現代の means “modern” or “contemporary”, so the original Japanese sentence even suggests that his music genre is trendy one. もっとも should be written as 最も in Kanji. My alternative translation is:
彼は最も偉大な現役歌手の一人だ。（かれはもっともいだいなげんえきかしゅのひとりだ。）
現役の (adjective) means “to actively engage oneself in his field” (i.e. not retired). 一人だ is in a present tense. Combining 現役の and 一人だ, you don’t need to translate “today” literally in Japanese.