I would defer to someone with greater expertise on the subject than me, but it’s worth noting for now that the Roman diplomat Priscus described him as "short of stature, with a broad chest and a large head; his eyes were small, his beard thin and sprinkled with grey; and he had a flat nose and tanned skin, showing evidence of his origin” (Sinor, Denis 1997). Given that Priscus met him in person, I suppose that its the absolute best a description that exists. There could be a primary source painting of some sort, either from the Romans or from the Han Empire, as historians believe the Huns and Xiongnu people to be the same group, but I am unaware if there is one.
While this doesn't reflect Atilla specifically, the early Huns were basically a mixture of Western Eurasian (Europid) and Eastern Eurasian (Asiatic) in their genetics. Western half came from Iranic nomads such as the Scythians, Eastern half from the East Asiatic tribes of the Xiongnu (which were a confederation of both eastern and western steppe people). As the Huns migrated westwards on the steppes they likely accquired even more western ancestry.
Here is a nice research paper about it. Scroll past the discussion header to see the charts, the green part is East Asian ancestry in those.
Keep in mind that Attila's historical description might have been somewhat skewed because his features would stand out amongst the "less asian" Huns or the Germanic Gothic vassals. I think that because of his lineage he might have had more Asian features than other Huns, but I think Attila likely would have looked like someone who has mixed European and Asian ancestry.