are you intrested in sport or selfdefence?
krav maga is good if you want to learn self defense, but not for competition.
judo/jiu jitsu is good for sport and selfdefence. BJJ mainly focuses on groundfighting, that is good for competition. Most of the other JJ syles (that I know of) focuses on selfdefence from standup possition.
As for diseplin and how effectiv what you learn is in real situations depends alot on what trainer you got.
Most gyms gives you a free lesson to try out the art, so go around to the diffrent martial arts gyms and try them out, you'll soon find out whats the right for you