There is no simple and absolute way of determining the most profitable coin to mine.  The biggest issue is that any coin that is the most profitable will immediately get a lot of mining power applied to it, which will drop the profitability rapidly.  The affect will be amplified on low volume coins.  So there are different ways of deciding which coin is the best to mine and whattomine.com can't be assumed to be the absolute arbiter on this.  Rapidly jumping from mining one coin to another will also hit profitability as most pools use PPLNS so it's hard to say with certainty if MPH method of choosing a coin is good or bad.