In my opinion, it really isn’t an either/or question as they serve different purposes. If your app has one set of operations a toolbar probably isn’t necessary as the operations can be accessed via the menubar. But if there are several sets of operations, then a toolbar might be the best way to switch between them, possibly with separate menubars for the operational sets.
For example, a program where you need to keep track of inventories, customers, and accounts might use a toolbar to switch between the modes and each mode might require its own set of menus.