I'd personally opt for monopoles. Angling them down will make them more localizable; having them fire straight across will make the sound more diffuse. Experiment to see what works best for your situation. Keep in mind that you want good left vs right separation in the surrounds, but you don't want them to be distracting.
Something else you may want to consider: have the surround speakers on either side of the couch, but pointing at the side walls. This way, you don't have to worry about wall mounting but the sound will still appear to come at you from you left and right. Just something to chew on.