If you are going to ask me then of course Tennis is not really that popular among the masses. Football on the other hand, it is the most widely played sport in the whole world and many fans do serious betting here. So you might want to do some research first and see which of these two you can actually be comfortable playing with. Also if you can check the analysis if the odd are fine and you will be able to hit the right team so that you can immediately win in your first try.