I would say most people will prefer the ring style for ease of sockets changes. Especially around the garage or at home. Plus it allows for the use and removal of non impact sockets.
Pin style are a must for most overhead work. The pin engages the hole in an impact socket for a secure connection.
But I don't believe any of the current Milwaukee 3/8 impacts are offered with a pin anvil.
Just the 1/2 inch brushed 2659, Fuel high torque brushless 2762, and the Fuel compact brushless 2755
There is also a ball pin version the Fuel 2655B and that's one of the ones I have. Similar to a ratchet ball concept its supposed to allow for tool less socket changes (but it always doesn't work that way though sometimes an impact socket need a little push to be released

) but it does give a bit more socket retention than a ring. Works for me around the farm not much a chance the socket will fall off if I need to go out in the field somewhere. Also works fine with non impact sockets too.
These seem to be being obsoleted though and hard to find stock is limited best I can tell. I would like to get another one still if I could as a bare tool.
And the pin version 2762 has different peak and mode #1 torque range than a 2763 so that is also something else to consider.