As I recall, I linked to an article on this topic some months or maybe around a year ago, and now with a new edition of Komodo on the market a new article has been written. The author addresses the big three engines: Stockfish 5, Komodo 8, and the aging but still worthwhile Houdini 4. His conclusion, in a nutshell, is that if one is engaging in serious, deep analysis and not just basic tactical checking then one should of course download Stockfish, as it's free, and if one must choose between Komodo 8 and Houdini 4 the former is the better choice due its positional strength.