With a mill it depends on what your thinking of doing with it
the bridgeports have an R8 spindle in them, this will not take big cuts
neither will something with morse taper spindle
as for lathes best to go and have a look at a few, all depends on how big you want to go with it, i can put a complete diff housing in mine end to end :006: its an old soviet toolroom lathe, if you want to do heavy work on a centre lathe look for something that has a bed width greater than its centre height , rigidity is the key with any machine tool