The ultimate goal of the survey is to find out actual results. The questions is how you can reach your respondents or participants? Most of the cases, I think you will not find the expected results from the online survey. I, my point of view believe offline survey is better and more reliable. Lets see others valuable opinion.
As mentioned, the goal is to get responses to the survey. If you have the time and resources to hand administer surveys and then hand input all responses, this will often lead to greater responses (assuming your population is in one location and available, such as school students who have a break in their day to take the survey). However, if for instance your population lives in varied geographic areas, then an online survey could be the ideal way to access responses. Good luck