I think you can hope at best opinions but not fully knowledgeable answers (unless game devs are part of this community). I answered Unreal cause It's a name that is recurring in the world of video games but in the end who can really say which engine is better. Once a game is made, the fact that the game is good or bad, graphically advanced or basic, bugged or finalized is up to the devs so I guess they alone can answer that question.

Most UE4 games look great while it seems nearly every Unity game looks/runs like fried shit

I don't know, it's very possible. I think I heard something about the Switch being compatible with a full version of UE4 or something so them using UE4 makes sense.

But the point here is: Will this new Yoshi game be better (or worse) than previous Yoshi games specifically because of UE4?

I can't agree or disagree with this, I'm not savvy enough in graphic engines but my question would then be: If games on that other engine are so bad to the point that players can see the difference why would professionals who develop those games use bad engines? Especially since UE is free to use...

(I think I heard it's free to use, in case it isn't, sorry I'm not up to date with those technicalities)

UE4 no contest.

although unity isnt as bad as people make it out to be.

Unity can create some pretty good looking games but don't forget it's a middleware engine. UE4 costs a hell of a lot more and for good reason. Unity is perfect for smaller developers. UE4 is perfect for higher-end development teams. As for those asking yes Yoshi is using UE4.

Context is king. An indie dev with a small, undemanding game who'd like the least effort required in porting to various platforms might be better served with Unity. A dev looking for more powerful tools ready to go out of the box would probably be better with Unreal. Cost and percentages are also factors to be considered that I'm not up to date with.

1. Probably UE4.

2. This is probably a more complex question than you realize. Unity is definitely much easier to learn, but it has its limits and if you need to go beyond those limits, it's probably easier to just use UE4 (unless it has similar limits in what you're trying to achieve).

3. This is a really bad question. If there was a simple answer, we wouldn't have them both. It depends.

Unity is great. You just need to pick the right tool for each job. Games like Cities: Skylines and Pillars of Eternity use Unity, and it works really well for them, which to me is proof that in professional hands, Unity is good. It's also used in games like The Forest, The Long Dark, Wasteland 2, Fallout Shelter, Ori and the Blind Forest, Firewatch, Cuphead, and Yooka-Laylee, so you can see it's not a bad engine. It's just that since it's easier to work with and has traditionally been the indie-friendly engine that is has also attracted less skilled devs.

UE4 performs better since the developers behind it also prioritize high end graphics but that's not saying much since it also ties itself down with lower standards such as mobile platforms, Unity is generally easier to work with if you want to do some simple flexible customizations while UE4's blueprint mode is fairly limited in that regard unless you actually want to learn C++ and which is better depends on the use case ...

I personally find both to be technically sloppy compared to specialized console centric engines ...