Combobulate is similar to Symex in its aims to be precise and intuitive. It differs in the style of interface and the feature set, providing a lot more grammar-aware and IDE-like features than Symex does. Symex has a minimal interface and offers more diverse features for elementary structural manipulation.
Ultimately, while there is some overlap in features, there’s also a lot offered by each that’s not present in the other, so that it might make sense to use one and cherry-pick features from the other. For instance, to employ specific Combobulate features from Symex, you could use a similar recipe as Symex and Evil. It may also be feasible to integrate them more at a library level. As part of the 2.0 release, Symex — a formerly monolithic package — was decomposed into small and modular packages in order to facilitate such goals.
Combobulate is thoughtfully designed and sophisticated, and may be a good fit for you. Try both and see which one (or both!) fits your style better!