Your Ex
The mere fact that you have that ex you can talk about does not just look good on soon-to-be relationships. Because it could rather make you look bad no matter what the ex did to destroy your relationship.
An ex is a potential threat to your date and if you talk about them, then it is the sign that you are not really over them and so dating you will mean to chase shadows. Do not think that you can paint your ex black by talking about them just so you look brightest.
It does not work that way. Instead of talking about your ex to send out signals to your date as to the kind of relationship you do not want, it is advisable to drop what you wanted in previous relationships. And even that is dangerous because it could scare them off too.
You have plenty of time to talk about your ex when you too are in a committed relationship but for now, you should just concentrate on getting to know each other. They are exes for a reason. The past. Concentrate on the now and the future.