We had a nice time at Marco's and Carmen's.
They are truly amazing people which will do their best to help you.
Location is perfect, the room was big and very clean and their flat is outstanding. Even if we arrived late they were available to welcome us and give us great advices on what to do in Valencia.
The only little thing that I quite didn't like was to share bathroom and toilets with 5 other guests, making it difficult if you really need to go to the toilet.
But overall we had a great time and I totally recommend this place to anyone staying in Valencia!