I've tried trading pairs both as mean reversion and trending. My research and experience tell me that mean reversion is the way to go (I only trade highly correlated stocks, not anti-correlated). I put on one unit, add one unit, take off one unit etc, trading only the same pairs every day and keep at least one unit 70% of the time. I only trade NYSE except for one Nasdaq pair. In my opninion Nasdaq pairs are not suited for pair, at least intraday.