Depends what film era lenses you're talking about.
Fast primes will be, in a lot of cases, stellar like the newer fast primes (a fair few of which seem to be based on old optical designs anyway).
But cheaper old zooms can be crap, I've got my dad's old solitel PK 75-150mm f/3.9 and it's quality is abysmal on my 40D.
But his other two lenses, a cosina 24mm f/2.8 and pentax asahi 50mm f/1.7 produce lovely images on my 40D. Easily comparable to my 150mm macro (a superb performer) for sharpness, let alone cheap kit lenses.
Some old lenses are among the sharpest you'll ever find.
I've never bothered with comparisons.