I would recommend some artists who compose and wrote lyrics for most of their songs, since the title of the thread is "artists that make good music", not "artists with the best vocal". However, they sing pretty well too, but not the best ones imho.
Jay Chou 周杰伦 has some really good music from around (2006 - 2012) imho, his music/songs were not as good in recent years. Melodies and lyrics are pretty much well balanced in most of his songs. His songs are often considered as classic or must-listen in the C-pop industry.
Recommend --- 青花瓷 , 魔术先生 , 阳光宅男
Wang Leehom 王力宏 has some very catchy music too. I recommend listening his fast songs over his slow ones. Melodies are mostly better than lyrics.
Recommend --- 在梅边 , 缘分一道桥 , Flow
Sodagreen 苏打绿 is awesome, especially with the unique voice of Tsing Feng's. The lead singer of the band is the one with best vocal from this list. If you are into lyrics, do check out this band's songs. Lyrics are most (if not all) by Tsing Feng and they are superb.
Recommend --- 燕窝 , 幸福額度, 他举起右手点名
Mayday 五月天 is good too, especially for people who are new to Chinese songs. Their songs' lyrics are easy to understand and meaningful at the same time. Pretty much perfect for someone who is new to Mandarin songs/ learning the language.
Recommend --- 2012 , 夜訪吸血鬼 , 如烟
Vae Xu Song 许嵩 --- My favourite at the moment and the least known from this list imo. Involved in the production of most of his songs, from composing to recording to editing. It is fun listening to his songs and trying to figure what story does the song tells, as the lyrics could often be interpreted in a few different ways.
Recommend --- 惊鸿一面 , 大千世界 , 在那不遙遠的地方