Of course it's a Deacon.
I don't know why everyone want to see a Xeno... It's a Deacon, the production wanted to put a Deacon, the Engineers created it. And now you will say that in Prometheus it was random circumstances, but no. Human genome and Engineers genome is the same, so same result. Moreover, the effects of the black goo show that every administration create a creature which have similar characteristics : acid for blood, elongated head, no eyes for example. David has just advanced the Deacon to create the Xenomorph. I don't know why everybody always want to find something to contradict that, maybe it's a problem because you don't like that but David create the Xenomorph, that's it...