We've discovered that the breakaway collars are useless in our house. They can pop them right off so they serve no purpose. Instead we get the collars with a piece of elastic on them so they can stretch. I've seen my cats get the stretch ones off of them, but they are much harder to get off that the breakaways. So knowing they can get them off if needed, but that they stay on the majority of the time works for us. All of my cats are indoor cats but they wear collars in case they get out. A few years ago one of my cats ran out the door late at night, and it took all of 30 seconds for him to completely disappear into the woods/swamp behind our apartment. Exactly 3 months to the day later, we got him back. We had put up fliers everywhere, called every shelter, talked to people by going door to door, but none of that got him back. In the end, a construction worker found him when he wandered into the construction site. He read his collar, called us and we got him back! I'm still amazed at that story, but for me that sealed the deal that mine will always wear collars. I know they can be micro-chipped, but I have some former ferals who have their ears tipped so my fear is that if one of them runs away, and someone sees them, the ear tip will make a person think they were just trapped, neutered and released and it wouldn't cross their mind to check for a microchip. The cat that ran away had an ear tip, so I'm so thankful that he had the collar on. The man who found him said that it took a week to earn his trust, but he kept trying because he could see that he was wearing a collar so he figured he had to have belonged to someone.
So my point is, mine all wear collars, but the stretch ones. They can get out of them, but they also stay on. One stayed on my cat for 3 months and its what got him back to us, so thats my reasoning!
ETA: The previous posters are right about the bells though. Mine have bells and name tags and when they are playing or just wandering around I can hear them, but if they want to hide, they'll hide. I'm amazed at how quiet that can be if they don't want to be found.