Probably better as an engineer. Quite a few people I've met working for the airlines have had a background in engineering and the airlines lean towards the more technical backgrounds. That being said, I have met an ex teacher who got a job flying an Airbus with minimal hours. At the end of the day, you would be better off being an excellent teacher than a mediocre engineer as you will have better examples of success to give when it comes time to sell yourself. I would choose whichever one you would rather do if the flying thing doesn't work out, as a lot of people go back to their old careers after training, due to an unfortunate lack of luck and timing.