Most people like to think that Madara took Hashirama's DNA because he wanted to have Rinnegan or Juubi, but I think it is not true. The reason is that everything related to Madara, Rinnegan and Juubi were accidental. I don't think such accident would be explained in the stone tablet, and I don't see why Rikkudo would allow someone to revive Juubi.
If you read Obito's flashback, that Ossan Madara was looking like a dead guy and he said many things:
1. After implanting Hashirama's cell, nothing happened until he was almost dead - this is an risky process and cannot be the result of a well explained recipe.
2. When almost dead, he unlocked Rinnegan, and broke accidentally the seal on the shell of the Juubi. He then named the that shell the Gedo Mazou.
3. You can use Gedo Mazou once you have Senju and Uchiha DNA - even if it is not perfect.
4. It is possible to use six path technique without Rinnegan.
While many there are many hint to say that Madara was after Rikudo's power, there are also a lot of uncertainty in how this power was attained. Besides, the fact that Madara had to give his eyes to Nagato in order to be revived while still alive is fishy.
The best explaination I can give to Madara taking Hashirama's DNA is Hashirama's power. Honestly, given what hashirama's cell can do, I think it is greater than Rinnegan alone. Besides, I think Rinnegan cannot work for an Uchiha unless they have a body like Hashi's or an Uzumaki body. This mean an uchiha with his base body cannot use optimally the Rinnegan - they don't have the life force required.