every martial art is effective in it's own way. it wouldn't have been invented otherwise.
the application is what matters most. what are you interested in hapkido for? MMA? self defence, or just a workout?
i train in kumo jiu jitsu and kickboxing. i do it because it's practical, and effective in ANY giving situation. MMA, self defence, etc.
before you get into any martial art, you need to think about why you want to start training in the first place. then do some homework on your options... and go from there