Personally, the best ones are ong, an/ian, ao, iu, ei/i,
The conjunctions are u, an/ian, iu.
Pay attention to the rhyme of entering tone. The pronunciation of many Rusheng words is different from that of modern Mandarin, so it depends on rhyme books. Generally speaking, the unqualified parts of metrical poems and words should be pronounced as entering tone, such as "The Yellow River is far above the white clouds". This sentence should be flat, and the quatrains can't be flat, so "white" should be pronounced as entering tone. Or yue Fei's rain on the railing, "rest" must be read in, otherwise it is completely unqualified. There is rhyme behind "Bai Xiang Ci Pu", which can be seen.