Thor with Mjolnir is more powerful by far -- its not even a contest. He can dimension dump the Hulk, probably energy siphon Hulk until he reverts, cast illusions that keep the Hulk busy then strike when the advantage is to be had.

Thor w/o Mjolnir is probably still more powerful than Hulk, with his storm generation and terrakinesis abilities.

In terms of power it is not a contest because Thor just has so many powers, all of which are used at really high level.

However, in terms of pure physical strength:

I think the classic model is that Thor starts out stronger than Hulk. But Hulk only escalates as a fight goes on, while Thor essentially stays the same. If it was purely hand to hand, Thor could win it in the first round with a quick KO. But if he doesn't, Hulk is gonna enrage enough that beating him mano-a-mano really isn't going to be an option. Mjolnir Thor can then respond by any of the options named above. Mjolnirless Thor is probably in more trouble.