One thing about vintage freewheels. I've used plenty of the two-notch freewheels in the past. I wouldn't go out of my way to get one now. Get one stuck, and they're a major pain.
The splined freewheels are much nicer.
If you do have a freewheel that uses a notched freewheel tool, then ALWAYS clamp the tool down tight to the hub with your QR before removing. I tend to do that with all freewheel and cassette tools out of practice.
As far as new vs old. The old freewheels seem to get pretty decent wear. However, the newer freewheels shift very nicely with the shift ramps and gates, and unfortunately seem to wear quicker.
It is easier to find new freewheels with 11T or 12T than vintage ones. But, it is much harder to find tight single step (corncob) gearing with the newer freewheels.
One may be able to adjust from 5 speed to 6 speed to 7 speed freewheels by changing the spacers on your hub and redishing the wheel.