Union is definitely more common in the US... it's not too common but definitely growing. My team is through my college and there are a surprising amount of colleges and universities with rugby teams. And there are also independent men's/women's clubs... multiple in my city. The US rugby sevens national team is actually pretty decent I think and just recently won some sort of championship (though I'm not sure against which countries it was played so that doesn't say much.) Before coming to school here I was only vaguely familiar with the concept of rugby. I'd never watched a match or played. So it's not that big in the US. I've even had people try to tell me that it's the same as American football or stupid things like that.