I have a handful of good old fifties, from the Jupiter-8 50mm f/2, Super Takumar 50mm f/1.4 & 1.8, Canon FD 50mm f/1.4. I love them.
But what really changed the game for me in normal focal length film shooting was a third party (!) Tamron 45mm f/1.8.
What did it have that the old ones didn't?
* Weather sealing
* Actual sharp results wide open (though stopping down to f/2.8 removes vignette)
* Three stops (!) of image stabilization so now I can use a fine grained 50 speed film where I was using a 400.
* 1:3 magnification with no extension tube