Theatre
So usually the place for the actor starving for artistic integrity in their work and satisfaction of a continous world taking on juicy roles that fill the soul while at the same time raising the audiences to individual elements of experience, is of course the theatre. Spelled "re" as opposed to "er". The two commone explanations for this is that the term "theatre" is the experience and "theater" is the place or venue. Then there is the dictionary reponse which basically says one is the original spelling for the European world (England) and then there is the "Americanized" spelling.
Anyway, to the point, think of any actor you admire that has astounding talent and draws your attention on the screen, whether they are speaking or not. Well, 9 times out of 10 that actor probably has the actor training of one from the theatre. Most actors who train in theatre schools or conservatories and focuses on the methods that are to create and allow stamina while at the same time maintaining realism, have more success in the film world as well.
As a director, of over 70 theatre productions, I have found it easier to work with actors who are outward and clear on their choices and I don't have to "pull" things out of them in rehearsal. This is usually evident with theatrical training. The depth of work an actor applies in theatre training is far more detailed and convincing than that of someone not digging for more in character and choices.
The styles of acting for the stage are different from that of the camera in that the technical elements aren't as demanding. In theatre you may be playing to a house of 400 and on camera you may have an intimate "couch scene" so by technical I mean the challenge of the body is more demanding in theatre to magnify those realistic ideas and emotions for the entire audience to experience, versus that of the camera where the microphone may be inches above your head and you can react in a "normal" voice, tone and articulation that only need to play to the camera.
The acting idea for every method always comes down to being as real as possible and living in "the moment" in order to make your character as believable as you can.
Theatre is usually more satifying for the actor because of the experience they have onstage with a live audience, but it ia also far more difficult to achieve than just being "fed" a line on a film set, which could be the process of a poorly shot movie. Not to say that film actors aren't as talented, on the contrary, most, as I said, have a theatre background and or strong training.
So once you have a theatre experience on a full stage and a satisfying production as an actor, you may be "bit" as they say, byt the acting bug and desire theatre more than any other medium