Hi Irving,
Personally I would not go for an MT3 spindle on a CNC mill.
1- MT3 requiere a serious amount of hammering to get the tools off, It is OK on a manual mill but on a CNC you are puting pressure and potentially damage to the ballscrew of the Z axis.
2- CNC Mill with MT3 spindle are difficult to find due to (1-)
3- A CNC mill is so much nicer with an auto tool change... Can't do that with an MT3.
4- You will need change tool in the middle of some G-Code, you don't want to have to hammer the tool at that point, you will loose precision.

Go for R8 or easychange .

RNR