http://www.itsmarta.com/getthere/sch...index-rail.htm
Omni/Dome/CNN Center stop = W1 on that map on the blue/green line
Vine City = W2 on that map on the blue/green line
It may be worth noting depending on when you travel, the Omni station has a lot more traffic to it, but that's not really a bad thing since there is more to see & do if you have time at that stop (CNN Center with awesome food court, etc...).
The one after it (on the other side of the Dome - Vine City) is a little more secluded & imho a less "safe" stop since it is kind of secluded.
This is just based on my personal opinion, & it isn't meant to scare anyone out of using the second Vine City stop.
I just know that less people get off & on the MARTA using Vine City than the Omni/CNN stop - & it's a quieter stop because of that.
I've used both with no problems, & like has been mentioned before, if you want to get to the pits, it's easier to use that Vine City one & walk around the GA Dome. Just head left around the Dome & you'll see the courtyard between the Dome & the GWCC as well as the entrance to the GWCC (pits).
You'll also see some amazing substructures around & under the GA Dome using the Vine City stop as well during your walk as shown here:
http://www.chiefdelphi.com/media/photos/18382