I've done both. Boxed amateurs for one fight for a year and then did No Gi BJJ for a bit. I'm looking to join a gym to only focus on one to master it and also I just don't have the time to do both. I love boxing and BJJ but also love to lift too, and I found while doing BJJ it was much easier to have success in the gym getting stronger. No matter how much I ate, boxing 4-5x a week while doing all the roadwork just hindered my gym progress. Boxing is by far the better conditioning sport IMO that one year I was in the best shape of my life. My goals are self defense and conditioning and possibly competing in either.