Barcelona remain the stronger side on paper and in matches like this the quality difference usually matters. Even away from home, Barça tend to control possession, dictate tempo, and create enough chances through sustained pressure and individual quality in the final third.
Valencia at Mestalla are never an easy opponent — the atmosphere alone can make matches chaotic — but over 90 minutes Barcelona still look like the more complete team. Valencia can be dangerous in transitions, especially if Barça overcommit, but consistency has often been their problem.
If Barcelona stay disciplined defensively and avoid gifting cheap counters, they should have enough attacking quality to break Valencia down.
Mestalla can absolutely make this ugly, but pure 1X2 logic still leans toward the visitors.