What is the correct model for enzyme-substrate complementarity?
This is true of all protein binding as well as the special case of enzyme-substrate interaction:

Various proteins are more dynamic than others: some have only one or two overall conformations and are relatively implastic otherwise. An example would be a receptor tyrosine kinase like Kit (or CD117, or Mast Stem Cell Growth Factor Receptor, whatever you want to call it), which has a very stable structure and binds its substrates in a lock and key manner.

Others, for example p53 (not an enzyme), have much more structural placiticity - even to the point of being mostly disordered when not bound. They tend to be induced fit binders (of other proteins, not catalytic substrates) and often exploit that to bind a broader range of possible targets than lock and key proteins.

The point is, it is a continuum between lock and key &lt;-----> induced fit rather than discrete classes you can sort proteins into.