Before I build a rig, I'm thinking of beginning mining with simply using the single card on a gaming computer.
If I had to choose would I be better off with an AMD RX 580 4GB or a Nvidia GTX 1060 3GB
I hear that AMD are slightly more efficient at mining but are more prone to overheating which isn't good.
Also, could I still use the computer for light tasks like talking to people on facebook or internet surfing while mining?
You should have no problem using the computer for light tasks, I do the same on my desktop while mining.