depend on products you want to sell, I think.. for digital products, it's better sell online, but phisical products some time better sell online or use both offline and online.. but both type of selling will need : market analizing, places (home, phisical store, server, etc) and the most important: marketing..
There are best businesses in the world both offline and online. There may come a business online tomorrow and turn as best business in less than a month and the same can even wind off another month later. This applies same to either online or offline business. So, there's nothing like a BEST business. There are good businesses around
Its depend on your interest and skill. For me forex day trade is my most profitable online business now.