From what I understand, with Canon, no lens made before the EOS mount of 1987 will function well on a modern digital body. The body has no system to meter exposure when using a pre '87, non EOS mount lens.
Nikon is confusing. There are some mechanical restrictions with some lenses made before 1977 and it may be that they also have light metering limitations when using other early 80's, F mount lenses.
Pentax might be considered to have the advantage in the lens legacy argument. Even a manual focus, third party lens made in 1975, will mount and meter light properly without adaptors of any kind to any Pentax digital single lens reflex camera. That is a lot of lenses to choose from in 35 years.
However, with Pentax's slip in market share even in the past ten years, it may be that Canon and Nikon are ahead in selections of modern electronically focused lenses for digital aspects.
I would not argue that, together the number of self produced and third party produced lenses over the last ten years for Pentax dslr would be less than either Canon or Nikon. But over a period of lenses available over 35 years... Pentax.
And image stabilization with a digital camera? Forget it. Pentax has that in the body so even one or two f stops can be gained from any 35 year old, MF lens.
My brother in law has recently asked my opinions in his search for a dslr which has given me an opportunity to research a bit.