I don't know very much about online high schools. But I think the best thing to do would depend on what you were planning to do after you finished one or the other.
Were you planning to go to college afterwards? Or stop with your high school diploma? And if you were going to college, where were you planning to go?
For example, community colleges don't care whether or not you have a GED or a high school diploma - they accept everyone and give you a placement test to make sure you have the right level of education you need. They have a wide range of classes at beginners levels so what people may have missed out on in high school, they can complete at community college before taking a more challenging course.
However, a university might be more picky about having an actual high school diploma since they don't offer such a wide range of beginning classes. The GED only tests to see if you have a basic amount of knowledge - it doesn't give you new knowledge or the knowledge you would get from a lot of high school courses. If you wanted to go to a university, it might be better to continue your high school education and learn as much as you can before trying to dive into that environment.
Of course, if you wanted to attend university, you could get your GED and do a year or two at community college to catch up to a university level. I did my first two years at a community college (even though I finished high school on time) to save money. So that is an option to.
If you are planning to stop your education after obtaining a GED or a high school diploma - I think many employers prefer that you have a diploma over a GED if that is the highest amount of education that you have, because like I mentioned above, they assume that you learned more and had more experience.
So what did you want to do after getting your diploma or GED?