I think a lot of people are betting on Chelsea. Same reason as you, they have a better team. Apart from that, from the history of eight matches, Chelsea won 5 times, lost 2 times and drew 1. The first leg took place in Porto, this is their superiority but remember Chelsea won 1-0 at Porto in 2009. Statistically Chelsea is very superior, but remember that is only history. Chelsea must continue to appear serious if they want to win, Porto has more power to make Chelsea lose,because they play at home.