You're talking about two entirely different things. The hook is the bit that grabs the needle thread, and arranges to stick a loop of bobbin thread into a loop of needle thread. You can have a rotary hook, where the hook rotates. That is, it goes around and around in one direction. Or you can have an oscillating hook where the hook oscillates -- it goes one way, stops, and goes back the other. Either can be arranged vertically, so the bobbin is loaded from the front or side. Either can also be arranged horizontally, so the bobbin is loaded from the top.
There are advantages of all arrangements. One of the big advantages of a rotary hook is that it can be driven faster, and with less vibration. The hook runs at a constant speed, while an oscillating one stops and starts twice for every stitch. The advantage of an oscillating hook is that it's usually a simpler mechanism. A horizontal hook lets you have a drop in bobbin, which are usually easier to thread, and on newer domestic machines is often under a transparent plastic cover so you can see how much thread is left on the bobbin. However, you can't replace the bobbin with work under the needle, and the thread path takes a 90 degree turn that a vertical hook doesn't, so some deal with strange threads not as well as vertical hook.
A machine with either type of hook and either arrangement of hook can be good at a particular opearation, or not good. There are other factors at work, too.
Are you having a particular problem? What is it? What sort of machine? What sort of material? What thread? What needle?