Goodness of fit metric to compare topic models NMF vs LDA
NMF and LDA models produce topic-word and document-topic distributions, so you can compare these models on evaluation tasks of topic coherence (i.e. evaluating topic-word distributions), document clustering/classification (i.e. evaluating document-topic distributions) or information retrieval (i.e. evaluating topic-word and document-topic distributions together). 

See some examples in "Improving topic models with latent feature word representations", "LDA-Based Document Models for Ad-hoc Retrieval".