MacBook or iMac, is there any speed difference between that 256GB, 512GB and 1TB options? And what about SSD endurance, does it differ in any way?
Assuming that you're talking about SSDs within the same generations of Mac, then capacity has no bearing on the speed, quality and/or expected lifespan of the components being used.
For example, the 1TB, 2TB and 4TB options of SSDs in an iMac Pro are the same as each other in terms of quality and performance. Likewise for the various SSD options in current models of 15" MacBook Pro and so on.
Where you will see differences are when you're comparing different drives, either because they're in different generations (or even types) of Mac models (e.g. 13" MBP v 15" MBP) or because they're a different type of storage device (e.g. traditional v fusion v solid state drives).