On my corpora, I am running LDA with different settings (I experiment with different number of topics, different different ngrams and TFIDF or regular BOW).
Now, I want to rank these setups to select one best topic model to continue working with.
In order to rank them, I have calculated both the coherence value as well as the perplexity for all the different settings, as is done here. In the link, the number of topics is selected using the coherence value. However, a rationale for why coherence is chosen is missing.
Therefore, I have a few questions: are there more common measures for this task? What are likely reasons for picking one of these metrics over the other?