The easiest tank to maintain is a square/rectangular one with a fully accessible open top.
The reason I personally don't like biorbs is that I don't like the restrictions the filtration system gives (can only use gravel), how much harder the filter is to clean comparable to an internal power filter, smaller surface = lower stocking capacity in relation to it's volume, small access hatch makes scaping/fiddling harder and restricts it more to a 'central' design, there is no 'back'/'safe place' for the fish to go which they will naturally look for even if they are confident and not looking to hide. Also the dimensions limit the fish as you shouldn't really be putting super active fish like danios in it.
Also it distorts the image of the fish which I don't like either. It's also harder to clean as it's a curved surface and because it bulges out it's harder to do stuff in it cause you tend to be stretching all the time (this may just be me as I'm only 5'3".
The reason I dislike the fluval edge is, limited stocking due to small surface area for gas exchange. Have to add a filter as it doesn't come with one as standard which totally negates the whole point of it which is 'wireless' 'no equipment visible' etc. Generally small tank so limited stocking even more (on top of the surface area issue).
The opening restricts maintenance again as it's small. If you ever need to catch fish it's a completely nightmare as they easily out manouvre you.
But overall I easily prefer it to the biorb.
So yeah... if I had to pick one it's the fluval. But there are so many better (from a fish and maintenance point of view) tanks than the two you've listed.
is it essential to have bottom feeders? This was another of my concerns with these tanks.
Not at all
You definitely don't need bottom feeders. And if you did want scavengers of some description then you could go with shrimp and/or snails in a biorb. But the point I was making was that even if you did want bottom feeders you couldn't realistically have them in a biorb... and there are alot of lovely bottom feeders I would have if I had enough tanks/space! lol.