I literally swapped from a barebones m340i to fully loaded f82 m4 last week because I had a chance to sell for nearly the price I bought at several years back.

M340 has way better low end torque and is better in city/suburban street driving. Smoother power delivery at lower rpms, chassis feels more stable. Launch is point and press. tech is way better if options are equal (duh).

Older M4 is much more raw and connected. Sounds better stock. faster when you get the revs up and both turbos going. Loves to throw the rear end out. On paper it’s slightly faster 0-60 but my butt dyno disagrees, wheels spin like road is icy. Maintenance going to be much more expensive. Also true “M” whatever that’s worth to you. Maybe will hold its value better past 100k miles/potential collectible.

I don’t think I can say one is objectively better than the other. The price is about even with a ~3 model year gap. It just depends on what you value more. There’s no objective answer. If my m340 was fully loaded I think I might say it’s better, solely from the smoothness of most driving situations and lower cost of ownership.