I tried both (and a bunch of other options) when Nova broke from an update. They were my two favorites, but ultimately I found I prefer Niagara's navigation I think.
I find it gets cluttered with too many apps. After like 40 apps Niagara can become a bit long to scroll through, especially when i can't remember an apps names half the time lol
Remembering app names is a must. Generally jumping straight to the right letter will let me open the right app with one click, it's only my "S" named apps that have enough apps to require additional any notable scrolling after jumping to the letter (I have 24 apps starting with S, and my screen only shows 15 apps max at once in the Niagara app list).
For all my most used apps, I put them in folders on the Niagara home screen for quick access. I also do this for apps like games where I want to view multiple options at once to decide between them. Anything I'm not accessing often needs some searching to find anyways.
I might have to check this out. I'm not sure how I feel about it being search based. But I do like the GPL license and it looks like it operates smoothly.