depends it was something short then I'd go with the anime , for example something like death note , less than 40 episodes and keeps you on the edge of your seat , the manga is good obviously but if it's something that's already finished I'd go with the anime to see the interactions and hear all the voices .
if it's something extremely long ( shounen jump mostly ) , I'd start with the anime and work myself up to the manga , the manga is always far ahead and with all the fillers , the anime is hard to follow , it's difficult to watch a filler when you know the story is head and it's out there , having said that I would still watch the episodes after a long time to refresh my memory or for the fight scenes since the it's difficult to see a fight scene in black and white
if it's something extremely long ( shounen jump mostly ) , I'd start with the anime and work myself up to the manga , the manga is always far ahead and with all the fillers , the anime is hard to follow , it's difficult to watch a filler when you know the story is head and it's out there , having said that I would still watch the episodes after a long time to refresh my memory or for the fight scenes since the it's difficult to see a fight scene in black and white
