I prefer to play GTA games online. I am really surprised if someone has not played online before. It is fun to include your friends in this game. Give it a try.
As far as I can recall there is also a Vice City mod for playing it online. Haven't personally played it and haven't even heard anything about it just came across it when I played SAMP.
Playing games online is more fun than playing offline or playing alone. I love to play games with my friends. There are a lot of features available online that cant is found in an offline mode.
Sometimes I like to play alone, if the situation calls for it. In general though I guess it is more fun to play with others online, but you do have to learn the people to avoid.