A machine learning laptop doesn't make a lot of sense - you won't find a laptop with a comparable GPU. Really, the answer is whatever you are comfortable working on - you'll be connecting to a server or AWS GPU instance to actually train any large net and generally writing and testing on a laptop. That being said, get anything with an NVIDIA card (for the time being everything runs on CUDA) or that testing will be done on the CPU, though perhaps there will be libraries supporting OpenCL down the road.