Comprehensive Recommendation
For this journey from Bressuire, France to Zaragoza, Spain, the most efficient and practical mode of transport is by air, as it significantly reduces the travel time to approximately 7 hours. Although train travel is a scenic and enjoyable option, it takes longer, around 12 hours, and can be more costly given the direct flights available. If budget constraints are a priority, consider the bus option as it is the cheapest but the longest (around 15 hours).
In summary, for a balance of time, comfort, and cost, I recommend flying with Air France or Iberia, especially if booked in advance. Alternatively, if you prefer the experience of scenic routes, a train journey with SNCF and Renfe offers a unique perspective.