In sports, there is always someone winning dominantly. It can get to a point where they are almost always expected to win. By that point do you continue to bet on those favorites to keep winning or does it bore you? Would you enjoy stirring it up a bit just for the fun of it and betting on the underdogs even if the chances are quite low?
In gambling, I believe everyone engaging in it wants to win, so I don't think anyone would like to lose their money on purpose, at least I will not want to do that to myself. Although sometimes I bet on the underdog, but I only do that based on the history of such game, probably the underdog are known for winning such dominant team. With this logic of mine, I still will not advice anyone to put their money on underdogs, because most times you end up losing your money.
In conclusion I think it's better you put your money on the dominant team, because your chances of winning is way higher than betting on an underdog.