Use == to test for a null reference, and the equals method to test a non-null reference for its value. Note that if you were to invoke any method, including the equals method, on a null reference, you'll get a NullPointerException.
rs.getString() returns a String. Unless you want to check for null on a String you should always use equals.
Remember that the <%= ... %gt; block can only output Strings to the JSP output stream, so the result of your statement must be a String or be capable of being converted into a meaningful String using toString().