For singers: what makes a good poem for art song?

In terms of sound, vowels are more mellifluous to sing than consonants and multi-syllabic words lead to fewer possibilities from a compositional and singing perspective. The fewer the syllables, the easier it is for collaborators to play with them. 

While vowel and consonant use might be interesting to think about in standard poetry, thinking about vowels and consonants is crucial for art song poetry. There is not usually a reason to pay special attention to vowels and consonants (e.g. in poetry workshops), which is why a poem that might be a good poem in one context may fit differently into art song.

What do you think?