Real Madrid (W) is showing impressive form, having made a confident start to both the Spanish league and the Champions League. The team hasn't conceded a single goal in its last four matches, demonstrating a rock-solid defense and complete control of the game.
Roma (W) is also showing good results, but the Italian team has been dropping points on the road. A recent cup defeat to Juventus revealed some inconsistency, especially on the road.
Given the home advantage, Real's motivation, and their current unbeaten run, the Madrid side have a clear advantage.