I tend to lean towards simple chord structures in my writing. I think that is a pretty big hallmark of most pop music nowadays. It can be very different from genre to genre. Yes, the beatles had some complicated chord structures, which at the time, worked pretty well. Those type of progressions would probably date a song out of being a modern pop song if you tried to go too far. I hate putting rules on songwriting, but that just seems to be the way that it works lately, and if you're writing towards a certain format, it's important to know the rules and characteristics of that format.