Archaea are interesting and often overlooked because they aren't numerous relative to bacteria. The domain Archaea always struck me as more of a "junk drawer" than a genuine grouping.
Why do you say that? They emerged from the large scale structure of 16S rRNA trees, which is what defined them as separate from bacteria.
http://sitn.hms.harvard.edu/flash/2014/origins-of-eukaryotes...