I can't definitively say what the first AI would look like because, well its down to whoever creates it first however there are some more likely designs than others.
Pop-culture tends to make AI look human I assume to add that extra fear of having a creation that looks and sounds like us yet is stronger, faster, smarter and so on. Though creating a computer in the shape of a human with working limbs is not an easy task as there is a lot to think about.
You first would want the machine to be able to actually move so it would need to have working joints that could move and rotate just the right amount so it appears to flow when it moves rather than having QWOP (the game) like movements. Then there would be the issue of designing the tech to actually fit in the shell, would you have the base of the machine all in the body and then just wiring around the limbs, it would also cause a lot of cooling issues as it would need some way to stop from over heating.
Human or computer?
I just feel that making an AI look like a human seems quite egotistical, it seems like going through a lot of unnecessary work to create the human shell and features, because it can't be for efficiency or maneuverability, but if you have some insight on that let me know in the comments.
I think the most likely outcome is that due to the immense complexity of creating true AI the first version will look relatively boring. It will probably be a very large computer similar to many you have seen before in an isolated building designed purely for creating and testing if AI can even created. Even if AI was created in say 2030 we would all likely never even see it, whoever created it, likely a large team working for a larger company, would have to be sure what they have created is actually AI and then they would try to use it to gain information for a while before announcing its existence to the world.
During the time they test and use it they might also create a body to put it in, so if we do see AI it could look just like any of us.
We are only just starting to figure out how our own brains work, so before we can create AI we need first understand how the brain actually works. There is then still the possibility of someone getting lucky...