Hi Ezzy,
Actually knowing whether a broker is a pure market maker or a STP broker, or even a hybrid of both is very difficult.
What you can do is call the broker and ask this directly. Whatever the broker's representative tells you, tell them that you demand to trade on a STP server and that they should commit to that. If they agree in writing - fine, if not think what your next step is.
ECN brokers are easier to tell - check my article on Forex Magnates to see
screenshots of Dukascopy or check the article about FXOpen's
ECN platform to see the unique features of ECN.
Also, ECN brokers are not too many and they are known. However, note that trading on ECN requires certain skills, is not for beginners and requires at least $1000 (this is the absolute minimum to open 1 deal).