On the one hand, the memory palace and the journey method are the same, in that you travel from one place to another, sometimes sequentially, sometimes not.
However, the difference is that a memory palace is an architectural entity, either real, virtual, or a combination of the two. It takes place, for the most part, inside some kind of building. An individual room of a palace suggests finiteness. So that in order to continue staying inside, you must either go into another room, or create another room, or create another palace entirely. It’s interior.
A journey is exterior. You find places along a specific route. It’s as open-ended as you desire, because the route can go on and on for as long as you like. You set your image in a place much as you’d do in a palace, and make the image interact somehow with, or be a substitute for, the place you set it.
As to which is better, well, who can say? What’s better for one person will not be as good for another person. There is nothing inherent in either the palace or the journey that makes it, for everyone, better or worse for storing information. It’s what you do with it (and how you do it) that matters. You put information along a journey and I put the same information in a palace. We both recall the information accurately. That’s the only thing that counts.