Best way is a league table. Like I said, Liverpool is better than Chelsea if we look head to head only, and even I disagree with that. This year we could have never managed to beat Barca. There are always match ups that favor different teams to the style. Liverpool matched up better to Chelsea than Barca. By no means does that mean Liverpool is better than Barca than. Barca's only real claim would be the head to head. Other than league matches, when did Real and Barca play? They split the league matches. Bayern only won on penalties, so not a real win. Penalties is a lottery. Chelsea the same in the final. They didn't lose the game, they lost the tie breaker.
This season with all factors built in, Real have to be the best. Past 3yrs, I'd agree with you Barca has been by far better than Real, but Real have closed the gap and edged them this season.