Neither has a lot ofg utility in AE. You'd buy one to make life easier in other applications... like Premiere Pro So what other applications do you use?
If you do not have an expensive 10-bit monitor go with the GeForce cards as they are much less expensive for equivalent performance. Besides the K4200 is only PCIe 2.0 and most GTX cards are the much faster PCIe 3.0
Geforce 900 series such as a 970GTX or 980GTX are the best card to get right now. That is what I would suggest.