How hard is Rugby or Ultimate Frisbee to learn?

I just transferred schools and am looking to join a club sports team to meet people and because I love sports. I played field hockey at my last college (club team) and soccer, but since I’ve played both of those for most of my life I wanted to try something new.

I’m trying to decide between Rugby and Ultimate and was just wondering which might me the easiest to pick up. (I know their both difficult, but just want a few opinions). I’m very athletic and have been involved in all kinds of sports and lifting since I was 8, so physical stamina not a problem.