I doubt he would buy any of them - more likely he will use an ahem version or the free/trial versions.Also, I have a fair experience with VMs. If you could tell me exactly what OS, apps, DBs etc. you are going to use, we can narrow down the choices together. Do you plan to purchase VMWare or will you be using virtualbox or would you buy Hyper-V?
I would suggest to have a minimum of 4C with higher clockspeeds as he is going to use for all in one, however for production VM - (more) cores over (minimum) clockspeed always.