I played through story mode to the end before venturing in to GTAO. I had no desire to play GTAO, but after finishing single player I liked it enough that I wanted more so checked out online to see what it was all about. Honestly, if it weren't for invite-only mode I probably would not have stuck with it. By playing that way I was able to rank up and kit-out in peace, so that when I go public now I'm prepared for it.
I really enjoyed the single player. The vibe, the satire, the action, the music, the heists and so many different activities. But I didn't like two out of the three characters, Michael and especially Trevor. Michael's a complete loser with anger management issues and Trevor is a psychosciopath. I liked Franklin though and wished that single player was just him. Since you can freely switch between them, I used Franklin for everything that wasn't related to missions tied to characters. All the free-roam stuff was Franklin.
If anyone is playing story mode and wants to maximize his profits, be sure to look in to how to play the stock market in conjunction with Lester's assassination missions. Doing it smartly will result in your characters having enough to afford anything in the game, even the golf course!
Animals flee this hell, the hardest stones cannot bear it for long. Only men endure