Don't get GTA 5 for Online.
Get it for the story, the story is probably going to be one of the best you've played. It's absolutely amazing, I've finished it like 3 times now and it's still so much fun.
Online is useless at this point unless you mod money. There's no way you're going to make money in online because almost everyone is a modder and they love to ruin people's life's, here let me give you a scenario: You're doing a mission in online, it's taken you 2 hours to already drive this truck for like 40 KM's, a guy come's out of nowhere with his Oppresor and one-shot blows you up. It's not as fun of a experience now unless you're playing races & stuff like that (people still mod with god mode & speed hacks).
Definitely worth it in my books for the story mode. - 10/10
Online? Not so much. - 2/10