I'm not sure if I should go dagger/dagger or dagger and magic. Are both decent?

dagger with the assassins blade while in sneak will be your bread and butter. Only magic for offhand would be illusion to be invisible. but shadow warrior negates this somewhat.

dagger, dagger.

Mehrune's razor, valdr's lucky dagger are both great. There's others out there.

One hand with dagger and the other hand for some illusion spell such as fury or invis.