As always, please give us complete sentences to consider. Also, please come up with something more likely than "XXX".
The way your question is split in half by the two suggested sentences makes the post messy. You could start with "Which of these two sentences is better?" or "Which is the better of these two sentences?"
You can use either of those.
Be aware though that there is sometimes a difference. As a generalisation, the most used is not necessarily the most often used. For example if you use item A ten times a day for two minutes, and you use item B once a day for two hours, then A is the most often used, but B is the most used.