I did BJJ for 6 months. During that time, the students and my teachers frequently came in injured (we had rotating teachers). Broken fingers, toes, sprained things, etc. Then one day one of the teachers was hurt so bad that she was out for awhile. I concluded that BJJ wasn't worth the risk of these kinds of injuries, especially ones that prevent me from working with my hands. Which is a shame because I loved how BJJ engaged the body and the mind, and the camaraderie with others.
One of the great things about bjj and judo, is that they are symmetric arts. That is, both participants have the same objective. This leads to a lot of intensity / realism within the rules of engagement.
This is also a downside, as some people get very caught up in winning.
By contrast an art like aikido is assymetric meaning that the participants have different roles and goals. You have an attacker, whose goal is to attack with energy and then fall safely. You have a responder whose objective is to avoid getting hurt by the initial attack and then to execute a technique. People work up to realism in a stepwise way that requires a great deal of pushing yourself psychologically. An upside of this approach is that there are relatively few partner-inflicted injuries.
Of course a downside is that realism, which is effortless in judo or bjj, takes a long time to achieve in aikido. It’s not uncommon to find dojos that never push toward intensity or realism—which is a (valid) reason aikido is frequently criticized by practitioners of other arts.
Both approaches are valid, and most marital arts are “effective” with respect to their own threat model. It’s mostly a question of whether you want an art where your Monkey Brain is called on to temper your competitive Lizard Brain (judo, bjj). Or, do you want an art where your Monkey Brain has to incrementally push your Lizard Brain to do things it is scared to let you do (aikido).
In my experience, the latter kind of art seems to yield fewer injuries at the expense of faster progress. At the right dojo, both will provide a positive social environment and as much fitness as you desire.
