Ok this is quite an important question for me. I have an answer in my head but is it turely what i belive? I am going to say online. Here are my thoughts.
Online is great and can never lose it's fun of the game unless you get bored of it. It is endless and you don't need to worry about any story lines or anyhting about or of that concept. If the game is not multiplayer this overtakes it and replaces it with online against people across the world. It's such great fun and i could never get bored of it as a person, yes take short break but no more than that. However. The downfalls appear to online gameing. If you are a holder of an X-BOX360 (BOOO) You may not get the problem as much as you do on a Playstation three format. LAG is a really big problem with online, if you are unsure of what lag is, lag is a game loading inside a game when it should be loaded. If you understand what i mean. It's where all the screen goes all jerky and play is paused for a split second and then reboots again. On a game called Motorstorm lag is very annoying. You see a car ahead of you jerking everywhere. You try to overtake it and it's jerk smashes into your vechile making you randomly flip and exploding even though nothing actually happened. On the opponents screen they will just see you blow up randomly because they don't know that they are lagging. This is a problem with online but don't worry it dosenn't happen all the time and it at least happens once on every online console. Another problem is Paying. This is a X-Box only feature so don't blame Sony. You have to pay i think £40.00 a year to just play online gameing. When on the PS-Three it's well...FREE! (notice the conflict). This is why i voted for Online. Does this mean Offline is really bad?
Now offline is the orignal game play and plan. With a great storyline and usually often better graphics than online. I will once again use Motorstorm as an example. On an Online race yoou may ride bikes and part of the system of riding bikes is punching players off them, it's so fun. However when you actually go to punch them off instead of actually well...punching them off it waits a few seconds then they fall of their bikes, making you unsure wheater to if you actually did punch them off. Now on an offline race against the computer opponnents as soon as you swing and hit they will fall of immediatley making it easy for you to ride on scared that they didn't fall off and hit you back. This is also a concept of LAG and on offline no lag is found because the game is fully loaded. The downward side of offline is that when you have completed the game then thats it. All the fun has been sucked out of the game and it's time to move on. Yes you can replay the levels but whats the point? You know what to do know what to do now, you know where to go and how to get there. It kind of ruins the total fun out of the gameing experience. Even though the game itself is so brilliantly planned compared to online, it still isn't perfect. Thats why i vote for online game play as this is much greater and their is endless fun unlike the real game.