They're totally different, but I know for a fact that Dostoevsky himself (as well as pretty much every Russian writer) considered Pushkin's talents far more advanced than his. Anyway, Dostoevsky was a novelist and Pushkin was a poet and dramatist, so it's like comparing T.S. Eliot to James Joyce (except in that example the novelist influenced the poet/dramatist rather than vice-versa). And besides, you can't make a statement like that until you read Pushkin in Russian. And without Pushkin there wouldn't have been Dostoevsky, Tolstoy, Turgenev, (possibly) Gogol, Chekhov, Lermontov... Russian lit as we know it would have been totally different.
I put Pushkin and Dostoevsky at the same level really, as when you get to that level of literary merit you can't say who's better. I love Dostoevsky because his mind is totally twisted, just as mine is, but Pushkin's technical skill (roughly 400 sonnets, all with the strange rhyme scheme I mentioned above and all of which flow beautifully? Do you have an idea how astonishing that is?!) as well as storytelling ability are dazzling.

