The non-determinist/one-box argument:
Omega has a reputation as near-perfect predictor.
If I choose only Box B, Omega likely predicted this and put $1,000,000 in it
Therefore, choosing only Box B will likely get you $1,000,000.
The determinist/two-box argument:
The money is already in the boxes.
Whatever is in Box B won't change based on your choice because the future can't affect the past.
Taking both boxes will always give me $1,000 more than taking just Box B
Therefore I should take both boxes.