Machine Learning library in Python, list or numpy or pandas
Pandas does normally a decent job allowing dataframes to behave as numpy arrays. 

My recommendation is to use numpy types, the reason is that, for consistency with pretty much what the industry is doing, you are much safer with numpy.

I love pandas, and I love the dataframes, but they provide extra functionality that the model does NOT need, the same way in general programming you will not use a String to represent a boolean (even though tou could do it with a String), simply because you should use whatever data types provides you the functionality you need... and nothing else.

So, numpy is the way to go. As for python lists, you do not get the mathematical operations that you get with numpy, so do not consider them.