As far as actual impact goes, Gaga is definitely the winner. Sure, Adele has been monstrous over the last year+ with her sales and awards, but does that translate directly to impact? Adele is one of my favorite artists and I love her dearly, but even I know her voice is a bit overrated. She was just a major breath of fresh air to the industry at the time.
I mean when Gaga is pulling off those strange scadals it is hard to compete against her.