A web page and a personal dialog need very different approaches. The big handicap of a web page is that I cannot lead a dialog but have to present my whole case in a monolog. Since I am not able to respond to the agreement or disagreement of my dialog partner I have to lay out the complete argument at once and can't ask questions without answering them myself on the same page.
For everybody it is much easier to accept as well as be impressed with that which he found himself, therefore it is so much more effective to ask questions and help others to discover facts than to just tell them.
Also, be sensitive. The suggestion that there are contradictions in the Qur'an is an attack on the most holy and central element of a Muslim's faith. If there is no need, I would prefer to not even mention the issue. But if the topic of the discussion moves in this way and the Muslim makes the property that the Qur'an is free of contradiction a major part of his argument, then you might want to have a few of them ready to talk about them.
But when you want to use some of the difficulties in the Qur'an, please make yourself thoroughly familiar with the argument first. Don't use it if you haven't clearly understood it yourself.
Second, reformulate it and make it a sequence of questions. Don't come up to a Muslim and claim that Allah said to Moses that he can find Muhammad mentioned in the Gospel and that is a clear contradiction since the Gospel does not exist in Moses time.
Rather take the information you find in the article "Moses and the Gospel?" and ask the Muslim to read the verses 155-158 and that if he could tell you who speaks to whom in each of these verses. Maybe you can even be so bold to ask if the wrong interpretation is possible: In 157 and 158 "unlettered" is mentioned, and since 158 speaks to Muhammad, doesn't that mean that 157 also have to speak to Muhammad? If the Muslim is fluent in Arabic or even has a clear perception of the English translation, he will deny and insist that 156-157 is spoken to Moses. After he has committed himself to that correct interpretation, THEN you ask the question whether it makes sense that Allah tells Moses that he can find Muhammad mentioned in the Gospel.
If he doesn't realize it, ask him "Whom was the Gospel revealed to?", and "When did Jesus live?" and supply the information if he doesn't know.
This way the Muslim himself will discover the problem, instead of you pushing it on him, and after he has committed that 157 is spoken to Moses, he can't really just change his mind after he has rejected the wrong interpretation already when you suggested it.
In a similar way, for any contradiction you want to use for yourself, reformulate it in a sequence of questions when you use it in a personal face to face dialog. Never give all the details away in the beginning. Leave some of it to strengthen your case after the Muslim will start to defend and try to explain it away. So, you will need some more material to back up your claim. On the web page, no interaction happens, and I have to give the whole argument away from the start.
But most of all, ask God that he will give you wisdom and love and sensitivity who to present these issues. We are not here to score points, but to win people. If you win the argument and loose the person then you have lost, not won.
Contradictions in the Qur'an
Answering Islam Home Page