I've been using various RPG Makers for nearly 20 years. I've tried to use different engines over and over again but none have really stuck as much as RPG Maker does, I just really love the software and it almost feels like it's become a part of my metaphysical being at this point.
Just picked up RPG Architect about a month ago or so. It's really good, and the developer is super responsive and always adds features. I had a particularly odd bug crop up trying to do something weird with the engine and although it took a bit of communicating back and forth to prove it was really an engine bug and not on my end, the dev was able to patch it up!
I think it has massive potential. It's definitely more complicated than RPG Maker is, but adds a lot of functionality to it. The dev's main philosophy for the engine is to make a version of RPG Maker that doesn't require plugins to do stuff that lots of users want to do with the engine. So it is super customizable. The layout and everything feels right at home as someone who has used RPG Maker for so long, but it does have way more things you can do with it.
The major downside compared to RPG Maker at the moment is that you cannot actually add your own stuff via plugins. Technically, MV and MZ are more robust if you're going to kit them out. However, it might cost you a bit more. The 3D settings being included by default is already a huge benefit and it is easier to make 3D games with it than RPG Maker. If you're REALLY looking into 3D as a feature though it might be better to check out something like RPG Developer Bakin.
There is also the fact that the engine, although it comes with default assets, they aren't as plentiful and varied as what RPG Maker contains. That includes not only music and sprites and things of that nature, but also pre-made skills, elements, items, formulas, menus, and all of that to help you get into making your game much more quickly. RPG Maker literally comes with everything you need to make an RPG right out of the box whereas RPG Architect has much more customizability and requires you to make everything from scratch. However, if you're going for custom stuff anyway, it's much easier to do with Architect and it's all in-engine.
If you're looking into game dev as more of a hobby or just starting out, then picking up RPG Maker MV when it goes on sale (which is pretty often) is going to be your best bet. If you have a bit more experience, and are cool with doing more stuff from scratch, then RPG Architect is a good one to go to. With the money you save, you can probably go out and grab some resources from Itch.io to help flesh out the assets. In its current state, I'd say you could make a full RPG with it and probably anything else you'd be able to do with RPG Maker as well. As time goes by it's only going to get better with more features. I think the dev is actually working on getting 3D model support in at the moment, so that's pretty cool! I've seen a lot of people in the Discord working with full 3D stuff and it looks pretty cool.
Another alternative, in addition to RPG Developer Bakin, would be RPG In A Box. It's made with Godot and you can actually export your games back to Godot. It mainly uses voxel graphics and you can actually create all of your voxel models/textures in the engine itself which is really awesome. It's pretty intuitive. They are releasing a new version soon (tm) that adds support for creating simple polygon graphics in the editor as well so that'll be cool to check out once it releases!
If anyone wants to know anything specific as far as comparisons go, feel free to ask! I've got a lot of RPG Maker experience and I'm learning how to use RPG Architect right now, working on a remake of an old horror game I made 11 years ago. I'm hoping I'll be able to use it for my future horror project and maybe even my next game after that! Locke, the developer, has talked about wanting to add a tactics battle system as one of the options, so as long as that's out within the next few years I'd be super happy to keep working with it.