M3 Pro (and some lower-core count M3 Max) parts have lower memory bandwidth than their M2 comparable. If your workload is highly dependent on memory bandwidth, then M2->M3 on Pro or Max might not be an improvement.

See tables here

https://en.wikipedia.org/wiki/Apple_M2#Variants

https://en.wikipedia.org/wiki/Apple_M3#Variants

On CPU/GPU benchmarks the M3 comes out ahead of the M2 (all flavors in like-for-like comparisons, plain, pro, max). However the M3 Pro and some M3 Max's have lower memory bandwidth than their M2 counterparts.

So a plain M3 is better than a plain M2. The top end M3 Max is better than the M2 Max. For the rest, you have to do a comparison and determine based on your intended use-cases, but for most people the M3 {Pro,Max} will be better than the M2 equivalent.