The way you rate a player is largely subjective. Speed in a winger is always a massive asset. But there are plenty of wingers that excelled without having blistering pace. Some would argue that those without blistering pace are better.
Some wingers excel due to being stronger, others more elusive, some just seem to have great ability to read the defence and the presence of mind to know where their support will be at all times. So to say one is ultimately the best ever to play for us is dependent on what you like in a winger.
For what it's worth I liked a number of them for us.
Hazem- Not the quickest or the strongest, but very elusive and in my opinion a great reader of the game which allowed him to excel when faster bigger or stronger athletes were beginning to dominate the game.
Utai- Also did very well despite not being lightning quick. He was fast, but the little bugger was a tank and had the strength to make up for his lack of height. Unfortunately he fell off a bit before the end of his career.
Halligan- Probably among the slower wingers we had, but was still quality. Get him within 5 metres of the try line and her find a way to reach out and ground the ball.
Dallas- Was very sad when he left the club. Absolute speedster with a bit of size about him. He was basically the prototype for what wingers are now.