I think Brady is the best QB of his generation, but there are many guys with bigger arms.
Brady has an underrated arm actually, but he'll never throw the ball as hard as Favre, Vick, Stafford or Rivers. I'd say he was about average or maybe just slightly above average for an NFL QB.
I would however say he was the most accurate (or possibly 2nd most after Brees) QB out there which is why a lot of his big hard throws seem to register in people's minds more often, simply b/c there are a lot more registers.