Which router spindle?

Hi everyone,
Can anyone help decide on which router spindle works best on a CNC build.
I'm not sure which make and model router would work best on any CNC router build, can anyone who as already done a build recommend one.
As anyone found a router that as a ER type collet, or as anyone made the conversion of there router to use the ER type collet.
Thanks in advance for any help.
Steve