An honest answer that draws on specifics about your situation will be a good start. It also has the potential to plant a few seeds for follow up questions during an interview.

Maybe your first airline experience was with that company. It's your hometown airline and you always wanted to work for them.

If you've been a customer and had a positive experience (or at least part of it could be described as positive). Maybe you already know pilots who work there and value their opinions.

In addition to any personal aspect you can blend in to your answer, use the strengths of the company to make the case for you. Get specifics on aircraft orders, route expansion plans, aircraft modernization, company financial status, stock price, etc. Do some research and find out all you can about the company and then use what you found to add meat to your answer (unless what you find happens to steer you away ;)). If you like what you find, buy some company stock. Doesn't have to be a lot, but being able to say you're a current shareholder is just another bit of ammo that might set you apart.