Finasteride prevent Test conversion to DHT, so it is efficient with test only, not only it shouldn't be used with Nandrolone (deca or npp) as it would turn nand into a very androgenic compound, but it is also useless with reducing existing DHT, therefore it is not of any help with DHT based hromones.
Dutasteride does exactly the same thing, except that it prevents two of the 3 isoforms conversion, instead of only one like Finasteride. Therefore, although it is more efficient than Fina, its way of action is strictly the same than Fina and thus is efficient only against DHT coming from test.
So, considering that Duta will basically do more or less the thame thing than Fina, that they have the same potential side effects (ED, orgasm disorder, libido disorder, ejacualtion disorders etc...), but that Fina got a 48H half life when Duta has a 4 weeks one, I would def go for Fina.
I would however play the topical card (Nizoral shampoo, Azelaic Acid) before using something as extreme as Fina / Duta. The side effects can be permanent and lowering DHT will hinder the cycle gains (DHT is anabolic).