Hi,
I have a 4" waste pipe stubbed out off my concrete basement floor. Is it better to install the flange over the pipe by chipping away the concrete around the pipe, or to install inside of the pipe?

You know we are going to say over just to make you do all that chipping. Really shouldn't make much difference.

Get yourself an Oakey Twist-N-Set PVC flange and put your chisel away.