Question about imperfect or preterite in spanish?

Do native speakers ever get confused on which to use?? Also, lets say I am in some convo in MX or something with a native speaker and I don't know if the thing I am saying takes the preterite or imperfect, rather than interrupt the convo by hesitating, which tense would be best to use? Like which is more common, the preterite or imperfect?