I think it's difficult to compare the talents of two artists who are not only polar opposites, but are also at different stages in their careers.
Adele is very conventional. Her songwriting and singing is very "safe", not that there's anything wrong with that, as it's amazing music. Gaga defiantly has a bit more "edge" and will take more risks in her songwriting, sometimes it works (Bad Romance), sometimes it falls flat on it's face (most of ARTPOP album).
For that reason I'm going to go with Adele, as she's A LOT more consistent than Gaga. I feel like Adele let's her music speak for itself, where as Gaga comes up with these artistic/philosophical explanations to sometimes distract from the fact it's just basic music with not much depth (again, most of ARTPOP suffers from this).
