There's only a couple of situations in the whole system where you are routinely forced to change trains to continue in the same direction. The only one of those that affects the airport is on the Red Line when traveling from north central Atlanta after 7:00 PM.

Travel time from Buckhead Station to the airport normally takes about 35 minutes if you can take the Red Line the whole way. If you have to change trains at Lindbergh, then it could take as long as 45 minutes to an hour. Track repairs are not routine, so delays due to maintenance don't happen very often.

In my experience (riding MARTA daily, both to my work and to the airport), I have found the service is generally pretty reliable. The trains are not as frequent as in more transit-dependent cities such as New York or Boston, but I would trust MARTA more for timeliness than I would a taxi or car service, even on weekends.

I have lived in Atlanta for my entire adult life (almost 40 years) and rarely do I drive to the airport any more. In most cases it's just a lot less hassle to take MARTA.

-JimG