Is Rin the original? or Len?

I think both. But Rin was realeased earlier. So, if there's an original, then it's Rin.

Rin was the original because Crypton wanted a female with a lower voice than Miku, but the demand for a male vocaloid was high, so they made a male voicebank using the same voicer and based him of Rin.

We'll both i think but rin was released before Len so yeah