Build quality would be very, very similar at this price range. Don't worry about defects, or faults in the mechanical sense. The speakers should last an aweful long time if not abused. Any performance issues should manifest themselves soon after you purchase them, well within the 5 year warranties (I believe Monitor audio has 5 years, Paradigm does for sure). Usually most problems happen in the first few months of usuage. I wouldn't really worry about either brand as far as quality goes...just whatever sound you prefer.