Fresh install or Cloning when migrating from HDD to smaller SSD (considering fragmentation, mostly)?
I'd advise just keeping things simple and clone it over if you can easily get your data down to the smaller size, otherwise do a new install and use Migration Assistant (not for any supposed performance benefits, just that it's simpler).

Fragmentation is not an issue with SSDs because the physical location of the data doesn't change the performance characteristics—each block has the same access time as any other, unlike a hard drive where it takes time to reposition the read/write head over the proper sectors.

In my experience the fresh install thing tends to be more of a Windows thing (and an older Windows thing at that). If you're experiencing specific performance issues, the consider a clean reinstall. But otherwise just clone or use Migration Assistant and enjoy the speed of a new SSD.