We go down every year and we have bought them in different ways:
1. Through Ticketmaster, but this option may be closed to you by now as tickets went on sale on 1/10, and they tend to sell out quickly.
2. Off ebay --- we have done this several times and have never had any issues. We have usually bought them from season ticket holders who won't be able to use their tickets for that game and we have ended up with some pretty incredible seats
3. Through Disney sports sales: disneysports.com/atlantabraves
We like to sit in the reserved seating area along the first base line. However, the stadium is small, so there really isn't a bad seat in the place.
Good luck and have fun --- this is our "most do" vacation every year!