Since this is an opinionated question, I'll give my opinionated answer: (TLDR is at the bottom with my final answer). Since you said GTA V, I'll give an answer to that, then to the online part. GTA V (which is the singleplayer) has a nice story and side missions. read more
GTA V; Two series have done more to popularize and advance the open world genre than any other: the Elder Scrolls series, and Grand Theft Auto. Much like Skyrim with the former, GTA V represents the pinnacle of the series, and is one of the best games ever created in the genre. read more
GTA 5. To start off the list, the game that we kind of grew up playing makes it mark. Grand Theft Auto from the early ages has been able to attract players from all around the world. From the time of the eagle eye view in GTA 1 till today, GTA had something for everyone. That is the main reason why GTA 5 become one of the best selling games in the world and obviously makes its place in the list of best open world games on PC. read more