Summary

Name/Basis	Pros	Cons
Full / Navigator-Based	Full-featured Ordered Set API Several kinds of iterators co-exist	Higher memory use [n pointers "wasted"] Complex operator algorithms
External / ADT-Based	Full-featured Ordered Set API All kinds of iterators co-exist Only way to get Levelorder	Bulky Iterators Levelorder is forward-only Preorder::Decrement = Postorder::Increment (and vice versa)
Threaded / Thread-Based	Most memory efficient Simpler/Faster Increment & Decrement Can still use ADT iterators for special purposes - set copy operations - data save order	Tree copy is costlier than usual - Set API is Singleton in std library

All iterator operations have amortized constant runtime

Except: destructors and copy operations for ADT-based iterators have Θ(n) runtime worst case