Well, technically - Any. ;-)
Hey there - I'm a new business technology trainer with 6 years experience helping new online business owners get off the ground.
If your goal is to make money quickly, then a service based business will be the fastest - you figure out what you can offer to whom, find them and then perform the service.
Info-products take longer to create and market, but have the appeal of, after the initial huge amount of hard work has been put in, leading to passive or residual income.
ECommerce and selling phyiscal products is the final way to go. If you have something that people really want, then it's just a matter of getting that in front of as many people as possible.
For ALL of these - knowing what you want to do (enjoying it is important - it's going to take a lot of time!), and having some idea of who is going to CARE about what you want to do, and WHERE they hang out is the best recipe.
Feel free to book a call if you want to chat in more detail. :-)