Love your portfolio. You should be with both. I'm not with Offset, but as far as I remember Offset doesn't require exclusivity, you can license on your own too. Also, Offset takes editorial, useful for stuff that you don't have model and property release.
I'm with Stocksy. Stocksy requires shoot/series exclusivity. You can't submit photos from the same shoot to other agency or license them on your own.
Both are picky, so what accepted by Offset, may be rejected by Stocksy and vice versa. So it's better to be with both if you are accepted by Stocksy.