Like many, I grew up around the formal, “Father surname”. Or simply, “Father” which I will still use today.
In my parish, we address our priests by their surnames…Father Zeheren, Father Hennen, etc. I have heard them introduce themselves to people as “Father surname”, so in that they give an indication as to how they prefer to be addressed.
We did have one priest, Father Puthemparambil (I think I probably misspelled that), and he preferred to be called “Father first name”. He was a much loved priest and if everyone who greeted him used his last name, he’d never get anywhere! It takes 10 minutes jus to SAY his name! I’ve found this to be the case also with other priests with long last names…they are Father first name.
I’d say that if you know the cleric’s title, but don’t know him personally, then use the formal title and let him correct you if he prefers to be addressed differently.
I often just call them “Father” unless I need to single them out for a particular purpose (ie if several priests are standing in a group).