The difference between ECN and STP jp markets is, on the ECN account, there is a commission per transaction; whereas on a standard account, you will be charged on spread. Both accounts work out similar in cost so it is all dependent on what you as a trader prefer.
However, JP Markets offers average spreads in the market. On average you can get EUR/USD for about 2 pips. I think JP Markets’ spreads are little higher compared to the other brokers.